How does a thesis statement aid the writer?

The thesis statement is the writer's point of view or opinion which he intends to support or prove in subsequent paragraphs.

So, how does it aid the writer? I suppose it serves as a roadmap/guide/focus for his ideas. 

1- cleans/ tidies up

2- were

3-would be

4- had known

5-takes

6-must be/ have to be/should be

x=4, y=4

step-by-step explanation:

y=2x-4;

x+2y=12

we can use substitution since the first equation is solved for y

where ever you see y in the second equation, replace it with 2x-4

x + 2(2x-4) = 12

distribute the 2

x+4x-8 = 12

combine like terms

5x-8=12

add 8 to each side

5x-8+8=12+8

5x=20

divide by 5

5x/5 = 20/5

x =4

we still need to solve for y

y = 2x-4

we know x =4

y = 2(4) -4

y = 8-4

y=4