If 988 includes 4% sales tax, we can use this equation to find the original price:
x + (x * .04) = 998
This equation tells us that a number, which, in this case, is the selling price of the item, plus four percent of that same number equals 998.
All we have to do now is isolate x.
x + (x * .04) = 998
Simplify.
x + .04x = 998
1.04x = 998
Divide both sides by 1.04
x = 959.615385, which rounds up to 959.66.
The selling price of the item was $959.66