A store sells 4 cans of nuts for $9. How much would it cost you to buy 7 cans of nuts?

First you need to find the cost of 1 can of nut:

let x represent the number of cans

4x=$9

divide both by 4

x=2.25

meaning 1 can costs $2.25

$2.25*7

=$15.75

meaning the cost of 7 cans is $15.75