To calculate Manny's earnings for working 4 hours as an aerobics instructor and 8 hours at the donut shop, you can use the expression \(21a + 12.50d\), where \(a\) is the number of hours worked as an aerobics instructor and \(d\) is the number of hours worked at the donut shop.
Given:
- \(a = 4\) (hours as aerobics instructor)
- \(d = 8\) (hours at donut shop)
Now plug in the values:
\[ Earnings = 21a + 12.50d = 21(4) + 12.50(8) \]
Calculating each term:
- \(21(4) = 84\)
- \(12.50(8) = 100\)
Now add the two amounts together:
\[ Earnings = 84 + 100 = 184 \]
So, Manny will earn $184 for working 4 hours as an aerobics instructor and 8 hours at the donut shop.