1- you have the equns as
10x+2y=7 and y=-5x+3
In either of the method you have provided as options are not able to solve this question. Suppose you put y in the first equation, it would give 6=7 which is not really desired and true of course. Thus these equations have no solutions.
2- As per the question let us assume the first candidate gets x number of votes and second y number of votes. Then you can write the equations as
x-y = 220
x+y = 810
Then add these to get x=515 and subtract to get y=295.
3- See if you assume l as length and b as breadth then you may get the equations as
If you solve these equations by what ever method you know you will get l=12 inch and b=5 inch