You want to find t such that
45 - 7t - 6t² = 25
or
6t² + 7t = 20
Solve for t. By completing the square, we have
6t² + 7t = 20
t² + 7/6 t = 10/3
t² + 7/6 t + (7/12)² = 10/3 + (7/12)²
(t + 7/12)² = 529/144
t + 7/12 = ± 23/12
t = -7/12 ± 23/12
t = -5/2 or t = 4/3
We ignore the negative solution, so the ball reaches a height of 25 feet at t = 4/3 seconds, or about 1.33 seconds after being thrown.
