hi i've been trying to solve a simultaneous equation and i'm sure i've gone wrong somewhere and would be grateful if someone could point out where:

i started by making x the determinant in the first equation then subbing it into equation 2 like so

(1)

then multiplied everthing by 5 to remove the fraction

then expanded the squared bracketed term:

then carried on with

then

i really don't think this is right, could someone explain this to me please? thanks