x + 3x + 6x = 400.
40 + 120 + 240 = 400.
x & 3 are simmiler terms. Add 3x and x to have a sum of 4x.
4x + 6x = 400
4x & 6x are simmiler terms. Add 6x and 4x to have a sum of 10x.
Divide each term by 100. ( in the equation.)
(10x )/(10) = (400)/(10)
Simplify left hand side: Canceling the common terms.
x= (400)/(10)
Simplify right hand side: Simplifying each term.
x=40
( The answer if solved would be 400 but this would be the simplifying way, if you know what I mean.)
Hope helps!-Aparri