The following given problem can be expressed in the form of:
E = 5.60 * T1 + 8.40 * T2
where,
E = total earning
T1 = normal hours worked
T2 = overtime hours
Assuming that the maximum T1 hours is 40 hours. Beyond that is considered overtime, therefore:
287 = 5.60 * 40 + 8.40 * T2
T2 = 7.5 hours
Therefore 7.50 overtime hours is needed.
