Final answer:
Opal will spend $372.
Step-by-step explanation:
To find out how much Opal will spend, we first need to determine the cost of one shirt. The display case states that 10 shirts are sold for $31. So, the cost of one shirt is $31 divided by 10, which is $3.10.
Now, Opal wants to buy 120 shirts. To calculate the total cost, we multiply the cost per shirt ($3.10) by the number of shirts (120). $3.10 times 120 is $372. Therefore, Opal will spend $372.