Answer :
ANSWER
I believe that the amount of the instant rebate is $30. X represents the price of the bike, and 0.09 is the sales tax.
So if the bike cost $100:
0.09(100) + (100-30) = 9 + 70 = $79
Although I think I would want them to tax the bike after the instant rebate and not on the original price.
If I'm wrong about the instant rebate then it would be 1.09x-30. Hope this helps.