I need help solving this practice problem, here is my work so far: 343N=(54.3 kg)(9.80 m/s^2)+(54.3kg)a. I am not sure how to continue this problem nor do I know if how I have this set up is right. The question is below:

A girl of mass 54.3kg stands on a weight scale in an elevator that is initially at rest. As the elevator begins to move, the scale displays a value of343N

What acceleration does the girl experience as the elevator begins to move? Assume that the positive direction isupward.

a= (blank) m/s^2