A helicopter, initially hovering 40 feet above the ground, begins to gain altitude at a rate of 21 feet per second. Which of the following functions represents the helicopter's altitude above the ground y, in feet, t seconds after the helicopter begins to gain altitude?

Explanation

Choice B is correct. It's given that the helicopter's initial height is 40 feet above the ground and that when the helicopter's altitude begins to increase, it increases at a rate of 21 feet per second. Therefore, the altitude gain t seconds after the helicopter begins rising is represented by the expression 21t. Adding this expression to the helicopter's initial height gives the helicopter's altitude above the ground y, in feet, t seconds after the helicopter begins to gain altitude: y = 40 + 21t.