Math Elimination Equations Algebra

I have the answers But i just needed to know how to get it by steps like show work? plus its not homework its just work that my teacher gave me but she wouldnt show me how it was misunderstanding actually

1. 2a - 3b = -11
a + 3b = 8

the answer is (-1,3)

3. 6x + 2y = -10
2x + 2y = -10

the answer is (0,5)

7. x - y = -3
x - y = 1

the answer is ( -1, -2 )

9. 3m - 2n = 13
m + 2n = 7

the answer is (5,1)


please show work and thank you :)!

Step 1. You can not solve a pair of silmultaneous equations with both letters present. To remove one of the letters you subtract of add the to two equations together when the amount of one letter is equal in both.

Taking question 1 as an example where both the eqautions contain 3b. You add the two eqautions together as -3 + 3 = 0 which leaves you with only the a values:

3a=-3

..because the b's added together give 0, the a's add to give 3a, and on the other side of the equation the
-11 and 8 add to give -3 (remember to add or subtract the entire equations, including both sides).

From here you can then work out the eqution you have left out as a normal equation to give:

Step 2. Next you subsitute this value in to only ONE of the origional equations. If we take the second equation from question 1 (a+3b=8) and substitute in, we get the following working:

-1 + 3b = 8
3b = 9
b = 9/3
b = 3

With question 2 it is very similar except you subtract the eqautions as they both contain +2y which will give 0, leaving you with just the x values.

4x = 0
x = 0/4
x = 0

Substitute in to one of the equations,

0 + 2y = -10
2y = -10
y = -5

Question 3,

Im ever so sorry, but im unsure on question 3, either I don't know or you may have typed it wrong.

Question 4,

4m = 20
m = 20/4
m = 5

Substitute,