7 (90-x) - 3 (180-x) = 30

180-x=3 (90-x) + 30

We move all terms to the left:

180-x - (3 (90-x) + 30) = 0

We add all the numbers together, and all the variables

-x - (3 (-1x+90) + 30) + 180=0

We add all the numbers together, and all the variables

-1x - (3 (-1x+90) + 30) + 180=0

We calculate terms in parentheses: - (3 (-1x+90) + 30), so:

3 (-1x+90) + 30

We multiply parentheses

-3x+270+30

We add all the numbers together, and all the variables

-3x+300

Back to the equation:

- (-3x+300)

We get rid of parentheses

-1x+3x-300+180=0

We add all the numbers together, and all the variables

2x-120=0

We move all terms containing x to the left, all other terms to the right

2x=120

x=120/2

x=60

So sorry if it's wrong I tried