A jet ski that holds 10 gallons of gas
 moves across a lake at a constant speed.
 When it starts, it is 45 miles from the shore.
 After 30 minutes, it is 30 miles from the
 shore. Which function describes the jet ski's
 distance from the shore?
 A. y = x/2 + 45
 B. y = - x/2+45
 C. y = 2x – 30
 D. y = -2x – 15