10. x-2y=3
4x-8y=12
Solving systems through substitutions means that you isolate a variable. You have one variable on one side and everything else on the other.
In the first one it's better to isolate the x and substitute it into the second equation. To isolate the x simply move -2y to the other side.
You get x=3+2y
And we're done with the first equation, now onto the second equation.
You can divide everything by 4 in the second equation so your second equation is x-2y=3
Substitute x into the second equation and you have that:
3+2y-2y=3
Or that 3=3 which is always true
Which means that in question 10 x and y can be anything.
Can you do the rest on your own?