Given that the height of the rocket at time t after it was launched is given by:
h(t)=-16t^2+115t+15
the height of the platform which the rocket was launched from will be given by the intercept of h(t), at the intercept, t=0 thus plugging t=0 in the function we get:
h(0)=-16(0)^2+115(0)+15
h(0)=15
hence the height of the platform is 15 ft
