Graph three variables in excel, and obtain a formula

Hello, I have three variables: temperature, pressure and time (for heating). I wish I could excel graph with two axes in "Y" axis and a "x" or as is most convenient, at the end I want to get a formula logarithmic or exponential.
data are:
Time Temp Pressure
20 20 9.5
15 30 10.9
10 40 15
I know that with a pressure of 20 psi and a temperature of 20 F, I need to heat the product 9.5 hours (time).
I would like to obtain the formula where I enter the pressure and temperature, and I get the time for heating.
Thanks in advance, Jesufer39

Graphing probably isn't necessary to the solution, except as a means of illustrating what the data look like. The data regression/curve fitting can be done directly in Excel using the various data regression algorithms available. The 2 methods I use:

1) If your expected function is "linear" (in the linear algebra sense so it can do much more than just straight lines/planes), then you can use the LINEST function to do a least squares regression.
2) If your expected function is "non-linear" or you want to use something other than a least squares regression, then you can use Solver to obtain the parameters for the equation.

So, the first question at this point is what form do you expect your equation to take?

Thanks you very much for your prompt answer.
This is the data that I really have:

Recta de Temp - Presion - Tiempo.jpg

And I need to know what is the steaming time with a known ambient temperature and different steam pressure of 20 PSI

Thanks in advance.

Unless I'm missing something, my response is still the same: decide on the form the equation should take, then regress the parameters of that equation from the information given.

I would add this additional observation: the latest data you've posted only shows data at a steam pressure of 20. The data contains no information for determining how steam time changes with steam pressure -- all you can really determine from the data is how steam time changes with temperature. If you need steam time at different pressures, you will need additional information (either as additional data or by making some intelligent assumptions) to determine the relationship between steam pressure and steam time.

Mr. Shorty, thanks for your help and time.

I just found the solution few minutes ago with the help of one of my co-workers as follows:

Steam Time = (Ambient Temp F *(-0.0967)+11.356)* 20/Steam Pressure

With the above formula, we can obtain the steaming time in hours, with any temperature in fahranheit and any steam preassure in PSI

Thanks again,and best regards,
JFbracho