To represent the amount, \( a \), Mike paid for buying 8 yards of ribbon, we can set up the working equation as follows:
\[ a = \text{(number of yards)} \times \text{(cost per yard)} \]
Given that Mike bought 8 yards of ribbon at a cost of $3.50 per yard, the equation becomes:
\[ a = 8 \times 3.50 \]
Now, we can calculate the total amount:
\[ a = 8 \times 3.50 = 28 \]
So, the completed equation is:
\[ a = 8 \times 3.50 \]
And the total amount \( a \) that Mike paid is:
\[ a = 28 \text{ dollars} \]
Thus:
- \( a8 = 8 \times 3.50 \)
- \( a = 28 \) dollars.