An elevator is moving with an initial velocity of 10 m/s downward with a 47 kg rider standing inside. What should be the final velocity of the elevator after 15 seconds of constant acceleration if the rider is to feel twice as heavy as he does when at rest? Upward is the positive direction.

Please follow the suggested sequence for arriving at the final velocity.

Step 1: What is the normal force on the rider during the 15-second acceleration period? What I did was: find the acceleration and multiplied that by the mass to get the net force. Then I subtracted the force of gravity from the net force to get the normal force. However there are two problems with my approach : (1) The steps I completed to find the normal force were seen further down the line of steps suggested for finding the final velocity (signifying that I did my process out of order) and (2) The answer was marked incorrect.

Please help, I am very confused.