Question

If 9x-3y=12 and 3x-5y=7 then 6x-2y = ?

Answer 1

x=12+3y/9
substitute in equation
3(12+3y/9)-5y=7
y=1/2
x=12+3*(-1/2)/9
x=21/18
substitute the value of x and y in
6x-2y=?
then,
6*(21/18)-2*(-1/2)=8

Answer 2

Given two equations  

9x-3y=12---(1)  

3x-5y=7---(2)  

First, we need to cancel out terms in x to find y

So multiply (2) with 3 and we get

3(3x-5y=7) = >9x-15y=21  

Now subtract 9x-15y=21 from 9x-3y=12

9x-3y=12  

(-) [9x-15y=21]  

9x cancels out  

-3y+15y=12-21  

12y = -9  

y = -34  

Substitute y in (1) and find x

$9x-3(-\frac{3}{4})=12$  

$9x+\frac 9 4=12$  

$9x=12-\frac 9 4$  

$9x=\frac {39} {4}$

$x=\frac {13} {12}$  

Substitute $x=\frac{13}{12}, y=-\frac{3}{4}$ in 6x-2y

$6(\frac{13}{12})-2(-\frac 3 4)=\frac{13}{2}+\frac{3}{2}=\frac{16}{2}=8$