My math final is tomorrow and I can't figure out how to do proportions with variables. I am allowed to use a calculator so that will be ok.

Proportions compare 2 things. For instance, if a questions asks how many cows can graze on 60 acres of a land if 15 cows can graze on 3 acres of land, we set up the proportion as cows : acres

15 : 3 = x : 60

Then convert the equation to a fraction:

cows/acres

15 x

___ = ___

3 60

Next, cross multiply by multiplying the numerator on one side of the equal sign by the denominator on the other side of the equal sign:

15*60 = 3x

900 = 3x

Divide both sides of the equal sign by 3 to isolate x

900/3 = 3x/3

300 = x