AT the movies, you order 3 boxes of popcorn and a bottle of water. the cost of the bottle of water is $1.75. your total cost is 9.25

Let x = cost of a box of popcorn.

3x + 1.75 = 9.25

Subtract 1.75 from both sides:

3x = 9.25-1.75

3x = 7.50

Divide both sides by 3:

x = 7.50/3 = $2.50