solve

Question

7x+5(-3x-4)=-21-7x
7x+(-15x-20=-7x-21
-8x-20=-7x-21
7 7
-8x-20+7x=-21
-1x-20=-21
20 20
-1x/-1 = -1/-1
x=1

Answer 1

ok, but I am puzzled by your lines such as
7 7 and
20 20

When you show solutions to equations each new line should contain an equal sign separating the left side from the right side.
Inserting such lines as you have interrupts the "flow" of equations from one to the other.

In my class you would have lost a mark for "bad form".