Cedric and zelda went shopping at price buster buster cedric bought to jumbo rolls of aluminum foil and three packages of aa batteries for a total cost of $21 zelda bought 5 identical jumbo rolls of aluminum foil and two identical packages of aa batteries for a total cost of $25 find the cost of one roll of aluminum foil and find the cost of one package of aa batteries

Let f and b be the cost of foil and batteries respectively.  We are first given that:

2f+3b=21  subtract 3b from both sides

2f=21-3b  divide both sides by 2

f=(21-3b)/2

Then we are given:

5f+2b=25, using f found above in this equation gives you:

5(21-3b)/2+2b=25

(5(21-3b)+4b)/2=25  multiply both sides by 2

5(21-3b)+4b=50  carry out indicated operations on left side

105-15b+4b=50 combine like terms on left side

105-11b=50  subtract 105 from both sides

-11b=-55  divide both sides by -11

b=5, since f=(21-3b)/2

f=(21-3*5)/2

f=3

So batteries cost $5 and foil cost $3.