
You multiple -7 by whats in the parentheses

(A negative number multiplied by a positive equals a negative number)
You then add 21 to each side in order to isolate the "x" or "-7x" by doing the opposite of the number which is -21

Combine the like terms

Now divide the number 35 by -7x (numbers are divided by "x")
35 divided by -7=-5
35÷-7=-5