Job estimating

I've got some data that I want to find the best fit for.
Basically trying to create a tool to estimate future job time.
For this particular situation we've broken it into two tasks, small jobs, and large jobs. Roughly taking 1.5h and 2 hours each
As we add more and more past jobs to the excel sheet I want to be able to get more and more accurate estimating numbers

Job	Small items	Large items	Hours to complete
Job 1	0	50	112
Job 2	117	123	370
Job 3	492	352	1120

Formula:

0*y + 50*x = 112

Formula:

117*y + 123*x = 370

Formula:

402*y + 352*x = 1120

As we get more inputs I'd like to keep adding to the data and find a more and more accurate value for y and x.

I've added the analysis add on to excel and there is so much try I was hoping someone could point me in the right direction.(If the analysis tool is what the right direction is).

Hope the goal and situation make sense.

Thanks

Jonathan