Calculus
posted by Elizabeth .
A hot air balloon headed due east at a speed of 20 miles per hour and at a constant altitude of 180 feet passes directly over an intersection. Find an expression for the balloon's distance d (measured in feet) from the intersection t minutes later.

since there are 60 minutes in an hour, the speed can be expressed as 20/60 mi/min = 1/3 mi/min
after t minutes, the distance traveled is thus t/3 miles = 1760t feet
using a right triangle, then it is clear that
d(t) = √(180^2 + (1760t)^2) feet