Answer:
See answers in explanation
Explanation:
For 1.)
A.)

For elimination, attempt to remove one variable. For these problems, the two equations can be added together without modification to remove y:

Now, substitute x for 6 in equation 2:

To check,

and

B.)

Substitute into equation 2:

For part 2, a manipulation must be made for each problem to eliminate a variable:
A.)

Substitute into equation 2:

B.)

Substitute into equation 2:

For question 3, both equations in each system must be manipulated to eliminate a variable:
A.)

Substitute into equation 2:

B.)

Substitute into equation 2:

I didn't write out all the checks, but all these answers satisfy their original equations. Hope this will help you out.