3x+4y=15 ( 1 ) and 2x-4y=30 ( 2 )
By Substitution:
Solve for x :
y = ( 15 - 3x ) / 4 ( 1 )
Substitute to ( 2 ):
2x - 4 ( ( 15 - 3x ) / 4 ) = 30
2x - ( 60 - 12x ) / 4 = 30
( 8x - 60 + 12x ) / 4 = 30 ( cross multiply )
20x - 60 = 120
20x = 180
x = 9 , y = 3
By Elimination:
3x+4y=15 ( 1 )
2x-4y=30 ( 2 )
First, eliminate y to get x by adding the two equations and the result would be:
5x = 45
x = 9
Eliminate x to get y by multiplying ( 1 ) by 2 and ( 2 ) by 3, and the result is:
6x + 8y = 30 ( 3 )
6x - 12y = 90 ( 4 )
Substract ( 3 ) by ( 4 ) to get the value of y, and the result would be:
20y = - 60
y = - 3.