To solve this problem you must apply the procceddure shown below:
1. You have the following system of equations:
x+y = 3
2x–y = 6
2. Then, you must clear the variable y from the first equation and susbtitute it into the second equation, as below:
x+y=3
y=3-x
2x-y=6
2x-(3-x)=6
2x-3+x=6
3x=6+3
3x=9
3. Therefore, the value of x is:
x=9/3
x=3
4. As you can see, the correct answer is:
x=9
