Final answer:
The total cost for the grapes that Caden buys is calculated by multiplying the weight of the grapes he buys, 3.9 pounds, by the cost per pound, $1.80, resulting in a total cost of $7.02.
Step-by-step explanation:
To find the total cost of the grapes Caden buys, you would use the expression that multiplies the quantity of grapes by the price per pound. Because Caden buys 3.9 pounds of grapes and the price is $1.80 per pound, the expression would look like this:
Total Cost = Quantity of Grapes × Price per Pound
Total Cost = 3.9 × $1.80
Calculating this, you would find that the total cost Caden pays for the grapes is $7.02.