Answer:
$72
Explanation:
Let's set up a proportion using the following setup:

We know that it costs $40 for 10 glasses.

We don't know the cost for 18 glasses. Therefore, we can say it costs
for 18 glasses.

We are trying to solve for
, the cost of 18 glasses. Therefore, we must isolate it.
is being divided by 18. The inverse of division is multiplication. Multiply both sides of the equation by 18.




x= $72
18 glasses cost $72.00