Caitlin works at a department store and earns $12.75 per hour. She has $42 removed from every paycheck for medical insurance. If her goal is to earn a gross of $633.75 in one week, which equation will help Caitlin determine the number of hours (h) she must work?
a.) $633.75 = $12.75h + $42
b.) $633.75 = $12.75h - $42
c.) $633.75 = $42h + $12.75
d.) $633.75 = $42h - $12.75