Let's rotate and redraw the figure to make it easier to understand:
The figure appears to be a right triangle with its hypotenuse and opposite side given.
Since this is a right triangle, to be able to get the measurement of the adjacent side, we will be using the Pythagorean Theorem:
The formula for the adjacent side or c is:
Let's now plug in the given values to get b.
Given: c² = 225 and a² = 145