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?

Answer: y = 40 + 21t

Explanation:

Apply the equation of distance covered.

d = vt + C

Where d is the distance covered

v = velocity, t = time

C = constant = initial distance covered

For the case above ...

d = y

y (t) = vt + C

But y (0) = 40 = C

C = 40ft

velocity v = 21 ft/s

Therefore, the equation of the altitude is given by;

y (t) = 21t + 40

y = 40 + 21t