Problem Solving

Jan lives x floors above the ground
floor of a high-rise building. It takes
her 30 seconds per floor to walk down
the steps and 2 seconds per floor to
ride the elevator. If it takes Jan the
same amount of time to walk down
the steps to the ground floor as to wait
for the elevator for 7 minutes and ride
down, then x equals
(A) 4
(B) 7
(C) 14
(D) 15
(E) 16

OA is D

Suppose there are x floors. 7 minutes is 420 seconds.

Then our equation will be:
420 + 2x = 30x
=> 420 = 28x
=> x = 15

Answer is D