Hello! So the formula for compound interest is P(1 + r)^t, where r = rate, P = principal, and t = time (years). C is out, because you multiply the rate and principal together to get the price, not add. You raise the decimal to a certain power, based on the amount of years. You add 1 to the rate. 5% in decimal form is 0.05 and you must add 1 to the amount, which eliminated B. The only answer that works is A, because it shows the correct formula. The answer is A.
Let α represent the acute angle between the horizontal and the straight line from the plane to the station. If the 4-mile measure is the straight-line distance from the plane to the station, then
sin(α) = 3/4
and
cos(α) = √(1 - (3/4)²) = (√7)/4
The distance from the station to the plane is increasing at a rate that is the plane's speed multiplied by the cosine of the angle α. Hence the plane–station distance is increasing at the rate of
(440 mph)×(√7)/4 ≈ 291 mph
