Let's define
x: months
If she stops making deposits and makes automatic $750 monthly, her account would have 5250 - 750x dollars after x months.
To find when the value of the account will be zero, we have to solve:
5250 - 750x = 0
5250 = 750x
5250/750 = x
7 = x
The value of the account would be zero in 7 months.