Let x be the number of sandwiches.
Since each sandwich has a cost of $6.75, then for x sandwiches the cost would be:
The change received is the difference between the amount used for payment and the cost of the sandwiches.
The difference between the amount used for payment and the cost of the sandwiches can be represented algebraically as:
This number must be equal to the change received. Then:
Solve for x. To do so, substract 50 from both sides:
Next, divide both sides by -6.75:
Therefore, the customer buys 5 sandwiches.