To find out how much Manny will earn working 4 hours as an aerobics instructor and 8 hours at the donut shop, we can use the expression given:
\[ \text{Total Earnings} = 21a + 12.50d, \]
where \( a \) is the number of hours worked as an aerobics instructor and \( d \) is the number of hours worked at the donut shop.
Substituting in Manny's hours:
- \( a = 4 \) hours (aerobics instructor)
- \( d = 8 \) hours (donut shop)
Now plug the values into the equation:
\[ \text{Total Earnings} = 21(4) + 12.50(8). \]
Calculating each part:
-
Earnings from aerobics: \[ 21 \times 4 = 84. \]
-
Earnings from the donut shop: \[ 12.50 \times 8 = 100. \]
Now, add the two amounts together:
\[ 84 + 100 = 184. \]
So, Manny will earn $184 working 4 hours as an aerobics instructor and 8 hours at the donut shop.