simultaneous equation, solved by substitution

7x-4y=28

2x-4y= -12

7x-4y=28, equation (1)

2x-4y= -12, equation (2)

isolate y in either one of the equations,

7x-4y=28 (1)

subtract 7x from both sides,

-4y=28-7x

^^ we will call this equation (3)

-substitute equation 3 into equation 2

2x+(28-7x)= -12

simplify

-5x+28= -12

subtract 28 from both sides

-5x = -40

divide both sides by -5

x= 8

subsitute 8 into equation 2

2(8)-4y= -12

16-4y= -12

subtract 16 from both sides,

-4y = -30

divde -4 from both sides

y=7

test on either of the original equations

7(8) - 4(7)=28

56-28=28

therefore,

x=8

y=7