Answer:
$72
Step-by-step explanation:
Let's set up a proportion using the following setup:
[tex]\frac{cost}{glasses} =\frac{cost}{glasses}[/tex]
We know that it costs $40 for 10 glasses.
[tex]\frac{40}{10 } =\frac{cost}{glasses}[/tex]
We don't know the cost for 18 glasses. Therefore, we can say it costs [tex]x[/tex] for 18 glasses.
[tex]\frac{40}{10} =\frac{x}{18}[/tex]
We are trying to solve for [tex]x[/tex], the cost of 18 glasses. Therefore, we must isolate it.
[tex]x[/tex] is being divided by 18. The inverse of division is multiplication. Multiply both sides of the equation by 18.
[tex]18*\frac{40}{10} =\frac{x}{18}*18[/tex]
[tex]18*\frac{40}{10} =x[/tex]
[tex]18*4=x[/tex]
[tex]72=x[/tex]
x= $72
18 glasses cost $72.00
