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