To find the total cost of eight pieces of bubblegum that were $0.20 each, you would multiply the number of pieces by the cost per piece.
Total cost = Number of pieces × Cost per piece
Total cost = 8 × $0.20 = $1.60
So, you can complete the sentence as follows:
"Zach bought eight pieces of bubblegum that were $.20 each; the total cost was $1.60."