Use a graphing tool to plot the equations:

The graphs of the given equations are shown:
As we can see, the graphs intersect at the point (3,27), which means that both equations have the same value when x=3, and in both cases, S=27 for that value.
This means that after 3 days, the number of items sold is the same for both cases. After 3 days, the number of items sold in both cases is 27.
Therefore, the answers are:
After 3 days, the total number of belts sold will be the same as the total number of wallets sold.
The number of belts and the number of wallets Mr. Matthew sold after this many days is 27.