If "x" is the amount Mark is paid per hour, then we need to multiply this by the number of hours he worked and add that to the tips to get the total earnings. This can be written mathematically as:
To know how much he is paid we need to solve for "x", to do that we subtract 15 to both sides of the equation:
Dividing both sides by 6:
Solving the operation:
Therefore, Mark is paid $11.5 per hour.