20% off means you pay 80% of the price so you multiply by 0.8, and 7% tax means you multiply by 1.07
Resulting cost = 18.99*0.8*1.07 = 16.26
Hope this helps let me know if im wrong!
The answer is x=6/11.
Tiger Algebra is a really good tool for algebra if you need some help.
Hope that helped! :)