Chapter 1, Equations and Graphs - Section 1.7 - Solving Inequalities - 1.7 Exercises - Page 149: 85

See below.

If the number of tickets sold is $n$, then: a)Then from the text: $n=120-\frac{P-200}{3}$ b) Our inequality is: $90\leq120-\frac{P-200}{3}\leq115\\-30\leq-\frac{P-200}{3}\leq-5\\-90\leq-P+200\leq-15\\-290\leq-P\leq215\\290\geq P\geq215$