algebra

I'm really confused on substitution. My teacher has a terrible accent and cannot understand what she says. i get the basics myself but i'm pretty confused on the following problems:
1) y= 3x - 8
y= 4-x

2) 2x + 7y = 3
x=1- 4y

3) x = 2y
4x + 2y = 15

Any help. I know i should probably know this by now. i started mid term :/

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  1. 3. Substitute 2y for x in the second equation.

    4(2y) + 2y = 15

    Solve for y. Put that value in the first equation to solve for x. Check by putting both values in the second equation.

    You can substitute either x or y value from one equation to the other to solve.

    Use these steps in doing the first two problems. I hope this helps.

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