Please help me with this question

Ifurniture stores having a weekend sale and is offering 20% discount on patio chairs and table the sales tax on furniture is 6.25 using function composition how can you represent the total amount a that you would need to pay for this furniture that cost x dollars

X+ y = 5 ; x - y =3 solve using linear combination

If x+y+z=0 what is the value of [tex] {x}^{3} + {y}^{3} + {z}^{3} [/tex]