13x = 79 ? can somebody explain #9 b. solve using the system of linear equations by elimination. i would love it if showed work.

8x + 2y = 44
5x + 2y = 35

Since 2y is already common, there is no need for multiplication. Just reverse the signs on the equation.

Like this; 

8x + 2y = 44
-5x - 2y = -35

All the additions become subtractions and vice versa.

-2y and +2y get cancelled.

Leaving;

8x = 44
-5x = -35

Now, subtract again. 

8x - 5x = 3x

44 - 35 = 9

So;

3x = 9

x = 9 / 3

x = 3

We found 'x' and now we have to find 'y'.

Just substitute. 

[8 x 3] + 2y = 44

24 + 2y = 44

2y = 44 - 24

2y = 20

y = 20 / 2

y = 10

Now, we re-check;

[8 x 3] + [2 x 10] = 44

24 + 20 = 44

Explaining the error for #9b is simply doing the whole sum. 

Hope this helped! :) I tried my best to explain.