Rebecca buys some scarves that cost $5 each and 2 purses that cost $12 each. the cost of rebecca's total purchase is $39. what equation can be used to find n, the number of scarves that rebecca buys?

Let n represent the amount of scarves Rebecca buys, and p represent the number of purses Rebecca buys.

We know that scarves cost $5 each, and purses that cost $12 each.  We also know that the cost of Rebecca's entire purchase is 39 dollars.

So, 

5n + 2p = $39

However, we were also given that Rebecca buys a total of 2 purses, so we can plug that into the equation.

5n + 2(12) = 39

When simplified, we get:

5n +24 = 39

To simplify even further, we must subtract 24 from both sides of the equation.

5n = 15

Finally, we must divide both sides by the coefficient of the variable, or 5.

n = 3

Therefore, Rebecca buys 3 scarves.

However, this problem didn't ask you to solve the equation, therefore the correct answer in this situation is probably one of the ones we started out with, either 

5n + 2(12) = 39

or

5n +24 = 39

Matt's volume would be 90 cm. cubed
Mindy's volume would be 90 in. cubed