Algebra POW HELP!!!!!
posted by Linda .
The cost of renting a bus to go snowboarding was split evenly by the 20 students planning to go. The day before the trip, 10 more students decided to go. Dividing the cost evenly among all 30 students brought the average cost down by $9.00 per person. What was the total cost of renting the bus?

Cost/30 + 9 = Cost/20
multipy both sides by 600
20 Cost+5400=30Cost
Cost= 540 dollars check that. 
what is the answer to pow4