Question 904309
A) set h(t) to 0  and solve
0= -16t^2+18t+13
*[invoke quadratic_formula -16, 18, 13, "t"]
t = 13/8
B) set h(t) to 4  and solve
4= -16t^2+18t+13
t=3/2
*[invoke quadratic_formula -16, 18, 9, "t"]