The function C(x) = 17.5x - 10 represents the cost (in dollars) of buying x tickets to the orchestra with a $10 coupon.a. How much cost to buy 10 tickets?b. How many tickets can you buy with $130?

a. How much cost to buy 10 tickets?
 For this case what you must do is replace the value of x = 10 in the given equation.
 We have then:
 C (x) = 17.5x - 10
 C (10) = 17.5 * (10) - 10
 C (10) = 165
 Answer:
 to buy 10 tickets cost:
 $ 165

 b. How many tickets can you buy with $ 130? 
 For this case we must make the substitution: C (x) = 130
 We have then:
 C (x) = 17.5x - 10
 130 = 17.5x - 10
 Clearing x we have:
 17.5x = 130 + 10
 17.5x = 140
 x = (140) / (17.5)
 x = 8
 Answer:
 You can buy 8 tickets with $ 130