SOMEONE JOIN MY Z"OOM I NEED HELP WITH MY MATH PROJECT

Acomputer store buys a computer system at a cost of $370.80. the selling price was first at $ 618, but then the store advertised a 20 % markdown on the system. answer parts a and b. a. find the current sale price.

Idon't get undoing if its pass adding and subtracting so can someone ? x-2 over 5 = 18

You eat $0.85 for every cup of hot chocolate you sell. how many cups do you need to sell to earn $55.25