To find the number of shoes the store had at the start, you will write the problem out and then work backward through this problem to solve for x, the starting amount.
If 64% of their inventory was sold, then 36% was not.
0.36x - 50) = 288; divide by 0.36 on both sides
x - 50 = 800; add 50 to both sides
x = 850
The store started with 850 pairs of shoes.