Final answer:
To determine how many months ago school started, we calculate the number of months by dividing Zach's earnings from babysitting ($400 after subtracting the one-time bonus from the total minimum earnings of $500) by his monthly babysitting income ($70), which results in approximately 5.71 months. Rounding up, we find that school started 6 months ago.
Step-by-step explanation:
The question is asking to determine how many months ago school started based on the earnings Zach has made from babysitting. Since Zach earns $70 a month from babysitting and received a one-time bonus of $100, we can calculate the number of months by dividing the total amount he has earned (> $500) by the monthly income from babysitting.
Let's assume the minimum amount Zach has earned is exactly $500 for the purpose of this calculation:
Total earnings = $500
One-time bonus = $100
Earnings from babysitting = Total earnings - One-time bonus = $500 - $100 = $400
Monthly income from babysitting = $70
Number of months = Earnings from babysitting / Monthly income
Number of months = $400 / $70
Number of months ≈ 5.71
Since we can't have a fraction of a month in this context, we would round the number of months to the nearest whole number, which is 6 months. Therefore, school started 6 months ago.