Mr. Valenzuela’s new bottle of shampoo contains 60 ounces of shampoo. He uses ounce of shampoo each time he washes his hair. Which equation can be used to find x, the number of washes after which 24 ounces will remain in the bottle?

For this case, the first thing we will do is identify variables:
 x: number of washings.
 y: amount of ounces of remaining shampoo.
 We write the equation taking into account:
 1) bottle of shampoo contains 60 ounces
 2) He used ounce of shampoo each time he washes his hair
 The equation is:
 y = -x + 60
 Then, for y = 24 we have:
 y = -x + 60
 24 = -x + 60
 We clear x:
 x = 60-24
 x = 36
 Answer:
 the number of washes after which 24 ounces will remain in the bottle is:
 36 washes.