There is $5691 in a store safe the manager deposit $2815 of that money into the bank choose the best estimate for the amount of money that is left in the safe

Choose the best estimate ??? that means there's a list of possible answers from which to choose.

Let's go ahead and estimate this ourselves:

Round off $5691 to $5700 and $2815 to $2800.  Subtracting $2800 from $5700 results in $2900.  That's a good estimate.