#### Answer

(a) Shows a sketch of a possible graph of x(t)
(b) Shows a sketch of a possible graph of y(t)

#### Work Step by Step

(a) The x-axis represents time in minutes and the y-axis represents horizontal distance travelled in miles. Assuming a constant speed, the airplane takes 60 minutes to travel 400 miles, and this is graphed as a straight line.
(b) The x-axis represents time in minutes and the y-axis represents vertical distance (altitude) travelled in miles. Assuming the graph here is non-linear, as the speed may not be equal at all points during the journey, the airplane takes 30 minutes to rise 6 miles and another 30 minutes to fall 6 miles.