i have a question. i am trying to find a function or some way to help me
interpolate a range of numbers to find a given value. say i have the range
of numbers below.

X Y
1 100%
1.5 90%
2 80%
2.5 70%
3 60%
3.5 50%
4 40%
4.5 30%
5 20%

Now i want to find the value of X that corresponds to a Y value of 65% now
obivioulsy the value is going to be 2.75, but say i have a harder range of
numbers is there a way i can do this.