Help locating x with given y in a line graph

For example I have a set of x and y coordinates like this

x = 1.2, y = 2
x = 2.6, y = 6
x = 3.2, y = 13
x = 4.8, y = 15
x = 5.9, y = 22

I put them into a line graph.
Then what I want to be able to do is pick lets say 2.25 on the x axis and have it return a value for y.
Any help on this matter will be greatly appreciated. Thanks in advance Andy.