According to the Pythagorean theorem, the square of the hypotenuse (the longest side) of a right-angled triangle equals to the sum of the squares of the other two sides. In this case, the ladder is the hypotenuse, which equals to the distance between the bottom of the ladder and the tree + the distance we want to find (x):
5² + x² = 13²
25 + x² = 169
x² = 144
x = √144 = 12.
The distance between the ground and the top of the ladder is 12 ft.
For this case we must find the solution of the following equation:

Applying distributive property on the right side of the equation we have:

Subtracting 7x from both sides of the equation:

Subtracting 20 from both sides of the equation:

Different signs are subtracted and the major sign is placed.

Dividing between -2 on both sides of the equation:

Thus, the solution of the equation is
Answer:

1. Make y the subject of the equation
y = -4 - 6x
2. Substitute values for guess and check
8 = -4 - (6 x 2)
8 = -4 - 12
This is incorrect.
2 = -4 - (6 x 1)
2 = -4 -6
This is incorrect.
-10 = -4 - (6 x 1)
-10 = -4 -6
This is correct.
The correct answer is C.