Answer:
a.

b.

Explanation:
a. We need to analize the information provided in the exercise.
We know that the ribbon sells for $2 per meter and a spool of ribbon holds 6.75 meters. Therefore, the cost of one spool of ribbon is:

Since the Craft club buys 21 spools, we can calculate the total cost by multiplying the cost of one spool by 21 spools. Then:

b. We know that one spool of ribbon holds 6.75 meters and the Craft club buys 21 spools, therefore, they amount of meters the Craft club buys is:

Since the club uses 76.54 meters to complete a project, we can calculate the amount of ribbon that will be left by subtracting 141.75 meters and 76.54 meters. Then: