We know the original price of the bike:
price_original=$89.75
In order to calculate the final price, we should calculate the following: original price-sale-coupon
The sale is 20%, which means: sale=20/100*$89.75=0.2*$89.75=17.95
The coupon is 10%, which means: coupon=10/100*$89.75=0.1*$89.75=8.975
The final price is: price_final=$89.75-17.95-8.975=$62.825