SAT Linear functions Question

$$h(t)=-16t^2+b$$ The function $h$ estimates an object's height, in feet, above the ground $t$ seconds after the object is dropped, where $b$ is a constant. The function estimates that the object is 40.96 feet above the ground when it is dropped at $t=0$ . How many seconds after being dropped does the function estimate the object will hit the ground?