This is a Pythagorean Theorem problem. Looking at it as a^2 + b^2 = c^2, you are looking for c , the hypotenuse of a right triangle. Setting this up on an x-y grid, one side, a , can be 13 - 3 = 10. The second side, b , can be 10 - 3 = 7. Then 10^2 + 7^2 = 100 + 49 = 149 = c^2. So, c = sq. rt. 149 = 12.2, your answer.
Using coordinate geometry , the Pythagorean Theorem becomes d = sq. rt.[ ( x2-x1 ) + (y2-y1) ] or d = [ (x2-x1 ) + ( y2-y1 )]^1/2. It’s just Pythagorean in more technical form. Study it; you will understand. NEVER STOP LEARNING!!
