I'm deeply sorry for my inconvenience. hopefully this is my last question. will someone ? (i forgot how to do taxes and discounts)

For discounts multiply the amount by the percentage. Then subtract your product by your amount.

For taxes do the same thing but instead of subtracting add your product to the amount.

1) C 49.75 
You just have to multiply by the percentage when it's a discount and subtract it from the original amount, 50% becomes .50. 99.50*.5=49.75   99.4-49.75=$47.75

2) D 103.48
You multiply by the percentage (0.04) and then add it to the original price when it's a tax

3) D 4.74
The same process as tax multiply by percentage (.2) and add to the original price

The difference between a markup and tax is the store controls the markups while taxes are usually state-controlled on a certain product (soda 5c or 10c tax is by state)