How do i solve two linear simultaneous equations 2x+y=7 & 3x-y=8 ?

To start with, try and spot whether or not two of the coeffecients (numbers next to the letters) are the same for either question (i.e. could be a 3x in one equation and a 3x in the other). This also works if the number is the same but the sign is different (i.e. 2x and -2x). As one equation contains a y, and the other contains a -y, you need to add the two equations together to eliminate the y, leaving 5x=15.

Dividing through by 5 leaves x=3, and if you substitute this back into either of the original equations you get that y=1.