Answer:
x=9
Step-by-step explanation:
combine like terms
4+5=9
9+6x=7x
to get 6x with 7x subtract 6x from both sides as its positive
6x-6x=0
7x-6x=x
9=x
21 cups
x=0
if something + 1 is 1, that means that 'something' has to be 0, and to make 2x 0, x has to be 0