You need to do proportions.
For this, I am going to set the numerator to only having prices and the denominator to only have the percentages.
170/80 = x/100,
where x is the regular price of the shirt, and the 100 is there because the regular price is technically 100% of the price.
So then we do cross multiplication and solve for x.
170(100) = 80x
17000= 80x
212.5 = x
So the bike's regular price is $212.50
