Answer:
___18___ classrooms
Step-by-step explanation:
Let the number of classrooms be x.
Each classroom uses 2 gallons, so x classrooms use 2x gallons.
They paint x classrooms using 2x gallons.
They still have 37 gallons left, so the entire amount of paint they had before they started painting was
2x + 37.
We are told they started with 73 gallons, so 2x + 37 must equal 73.
The equation is
2x + 37 = 73
Now we solve the equation.
Subtract 37 from both sides.
2x = 36
Divide both sides by 2.
x = 18
Answer: ___18___ classrooms