To determine the opportunity cost of Sergei's best decision, we first need to identify which job he would choose to maximize his earnings.
- Raking leaves: $50
- Making deliveries: $70
- Babysitting: $65
The job that makes him the most money is making deliveries for $70. The opportunity cost is the value of the next best option he is forgoing by making this choice. The next best option after making deliveries would be babysitting, which pays $65.
Therefore, the opportunity cost of choosing to make deliveries (the best decision) is the earnings he could have made from babysitting, which is $65.
So, the correct response is:
$65