The television cost $289.90. the sales-tax was 8%. how much was the sale tax on the television?

Let us look at it this way, if the net price of the television was $100, add the sales tax at 8%, would make the sale price $108

so, in other words, if the sale price is $108, then the tax is $8
therefore, the sales tax was 289.9 (actual sale price) / 108 (sale price we had in mind if the price was 100 and sale tax was 8) x 8 (the sale tax in percent) = $21.47