x + 2y = 50
-2x + 3y = 40
5x + 5y + 5z = 300
================
x + 2y = 50 ....multiply by 2
-2x + 3y = 40
--------------------
2x + 4y = 100 (result of multiplying by 2)
-2x + 3y = 40
------------------add
7y = 140
y = 140/7
y = 20 <==
x + 2y = 50
x + 2(20) = 50
x + 40 = 50
x = 50 - 40
x = 10 <==
5x + 5y + 5z = 300
5(10) + 5(20) + 5z = 300
50 + 100 + 5z = 300
150 + 5z = 300
5z = 300 - 150
5z = 150
z = 150/5
z = 30 <==
solution : (10,20,30)...x =10, y = 20 , z = 30
