Answer:
$69,000 per year
Explanation:
the total economic cost of going to college = college expenses + implicit costs
total economic cots = $30,000 + $90,000 = $120,000 / 5 years
if you want to recover your college costs in 5 years, you will need to recover $120,000 / 5 = $24,000 per year
so you would need to earn = $45,000 (old salary) + $24,000 = $69,000 per year
*opportunity costs are the additional costs or benefits lost from choosing one activity or investment over another alternative.