Zippy's economic profit is $80,000.
Economic Profit = Revenues - (Explicit Cost + Implicit Cost)
Implicit cost or opportunity cost refers to the loss an individual incurs from an alternative decision, as a result of making a decision.
In this question, Zippy's implicit costs are the $30,000 from his job at Joe's car repair.
Additionally, he loses the 10% interest he would have earned on his savings of $150,000 had he not started his business.
So Zippy's implicit cost is $45,000 ($30,000 + $15,000)