Although the information has been presented in a baffling way in this question, but I think I understood the expressions.
We have been given that price of monster truck is x dollars and there is an 13% monster truck tax.
We can express the monster truck tax amount as
.
Therefore, the total amount including tax will be
.
We can now match each statement with its equivalent expression as shown below
The price of Camacho’s new truck before tax = x
The amount of tax Camacho pays = 0.13x
Camacho’s total bill for the monster truck = 1.13x
None of these = 0.87x
There are 49 gallons of red paint.
I figured it out by doing the following:

If you subtract the gallons of pink paint (21) from the total number of gallons (70), then you get the number of gallons of red paint (49) because 49 + 21 = 70. I hope that helps :)