Question 179454
Assume the tree is vertical and the triangle formed by the rope,tree,ground is a right triangle. You can use Pythagorean theorem {{{a^2+b^2 = c^2}}} where the rope is c. Or you can remember the a 3:4:5 triangle is a right triangle.

In this case one leg is 48 and the hypotenuse is 60. So you have an X:48:60 triangle. That is the same ratio as a 3:4:5 (12 times bigger, but still 3:4:5. Since 12*3:12*4:12*5). So the other leg is 12*3 or 36