Develop an expression for the number of snacks:
say that P is the number of pretzel bags,
C is the number of cracker bags
To get a snack for everyone, the number of bags of all snacks (C + P) needs to be equal to the number of people.
C + P = 12
We don't know the number of bags for each crackers and pretzels right now, but we do know the cost per bag and the total maximum cost
Pretzels are 1.50, crackers are 2.00, max total is 20.00.
Remember, we are saying that "C" is the number of cracker bags purchased, so the total cost of all cracker bags will be (2.00 * C). Likewise, at 1.50 per bag, the total cost of pretzels is (1.50 * P).
Adding the two costs together yields
(cracker cost per bag) * (number of bags of crackers) + (pretzel cost per bag) * (number of bags of pretzels) = (total cost of all snacks)
($2.00) * C + ($1.50) * P = $20.00