Hint: You might find Pythagoras' theorem very useful [a^{2} + b^{2} = c^{2}].

Answer: 148 inches.

We can use Pythagoras' theorem if we draw an imaginary line across to create a right-angled triangle.

The hypotenuse is equal to the rope's length R. The bottom of the triangle is 48 inches. The vertical side is R - 8 (the difference between 20 inches and 12 inches).