The answer is 57.04 meters.
Solution:
The height y of the rock above the ground as a function of the horizontal distance x from the starting point on top of the hill can be modeled by the equation
y = -0.04x^2 + 1.3x + 56
We now set this equation equal to zero because the height of the ground where the rock will land is zero:
0 = -0.04x^2 + 1.3x + 56
Since we have a quadratic equation, we can calculate for the horizontal distance x by using the quadratic formula
x = [-b ± sqrt(b^2 - 4ac)] / 2a
x = {-1.3 ± sqrt[1.3^2 - 4(-0.04)(56)]} / 2(-0.04)
x = (-1.3 ± sqrt(10.65)) / (-0.08)
x = -24.54 meters or 57.04 meters
There are two solutions for x but one is negative, so we choose the positive value.
