Finding corresponding coordinate based on known ordered pair

Question

I need to know how to find the corresponding Y coordinate based on a given X coordinate that lies between two ordered pairs.

Example:

(60,25) and (70,40) Find the Y coordinate that corresponds to a X coordinate of 65

Answer 1

If the function is a straight line between two points $(x_1, y_1)$ and $(x_2, y_2)$, then the corresponding value for any $x$ is this equation

$y = y_1 + \frac{x-x_1}{x_2-x_1}(y_2-y_1)$.