To find the amount \( a \) that Mike paid for 8 yards of red ribbon, you can set up the equation based on the cost per yard.
- The cost per yard of ribbon is $3.50.
- Mike bought 8 yards, so the total cost \( a \) can be calculated as: \[ a = \text{(number of yards)} \times \text{(cost per yard)} \] \[ a = 8 \times 3.50 \]
Now we can solve for \( a \):
\[ a = 8 \times 3.50 = 28 \]
So, the completed working equation is:
\[ a = 8 \times 3.50 \]
Thus, the solution is:
\[ a = 28 \text{ dollars} \]
If you want to rewrite this in terms of \( a/8 \):
\[ \frac{a}{8} = 3.50 \]
So you have:
- \( \frac{a}{8} = 3.50 \)
- \( a = 28 \) dollars.