$1,100
To solve for how much the grocery store employee will make for working 55 hours, we first calculate the earnings for the first 40 hours worked: $15 * 40 = $600.
Then, we calculate the additional earnings for the 15 hours worked over 40 hours: $20 * 15 = $300.
Adding the two amounts together, we get $600 + $300 = $900.
Therefore, if the employee works 55 hours, he will earn $900 for the week.