Patti works as a waitress. She earns $4.50 per hour plus tips and serves an average of 6 customers per hour. If Patti earned $108 during an 8hour shift, which amount best represents the average tip per customer? The answer is 1.50, but how do I solve for this?

her wage was $36
subtracted from $108 leaves $72 in tips
she served 6x8 = 48 customers
$72/48 = $1.5 tip per customer
subtracted from $108 leaves $72 in tips
she served 6x8 = 48 customers
$72/48 = $1.5 tip per customer

she sounds like a prostitute.