Math
posted by Bob .
For a class play, student tickets cost $2 and adult tickets cost $5. A total os 30 tickets were sold. If the total sales must exceed $90, what is the miniuim number of adult tickets that must be sold?

Let s = # student tickets and a = # adult
s = 30  a
2s + 5a > 90
Substitute 30a for s in second equation and solve for a. Insert that value into the first equation and solve for s. Check by inserting both values into the second equation.