Question

(3x+20)+(7x+50)=90 Solve for X

Answer 1

Combine your like terms.
So 3x + 7x 
and 
20+50

Write your new equation and equate it to 90.
Put everything numerical on one side and the other ( the unknown aka the x)
to another side of the equal sign.

Answer 2

(3x+20)+(7x+50)=90

x=2