solves 2x +3y=40, 5x +2y=34

You have three options
1) re-arrange them into y=mx + b format, then graph them and see where they cross
or
2) re-arrange to get 1x or 1y alone in one equation and "sub" into the other equation. This is by the substitution method
or
3) Use the elimination method.
In that method you multiply one or both equations by a number so that when you add them up (or subtract them) one of the variables would be eliminated.
In this case... suppose you want to eliminate the x's
If we multiply the first equation by -5, and the second equation by 2 we obtain
-5(2x +3y) = -5(40) that is -10x - 15y = -200
while
2(5x +2y) = 2(34) gives 10x + 4y = 68
When you add these up you obtain...
- 11y = -132
divide both sides by -11
and you have y = 12
now sub that back into one of the originals and solve for x : )

Eq1: 2x + 3y = 40
Eq2: 5x + 2y = 34
Multiply Eq1 by 2 and Eq2 by 3.
Then subtract Eq2 from Eq1:
4x + 6y = 80
15x + 6y = 102
Diff. -11x = -22
X = 2.
In Eq1, replace x with 2 and solve for y:
2*2 + 3y = 40
Y = 12.

I don't understand

I DONT UNDERSTAND IT

I wont subsitision method