Two eighth-grade classes are selling popcorn to raise money for an end-of-year field trip.
One class is selling popcorn for $4.50 a bag and has already raised $270.00.
The other class is selling popcorn for $5.00 a bag and has already raised $250.00
Write an equation that can be used to calculate p, the number of additional bags of popcorn each class needs to sell, so that the total amount raised is the same for both classes.