1.) The product of five and a number is equal to the difference of five and another number

Answer 1

5x = 5-y

y+5x = 5

UNLESS you meant

5x = l5-yl where the "difference" is positive regardless whether y>5 or y<5

then

5x = 5-y if 5>y

but 5x = y-5 if 5<y