What operation is used to isolate the variable

Well it all depends how you wanna isolate the variable see now look below ↓

Put every term that contains the variable on one side of the equation and every term that does not contain a variable on the other side like her demonstrated beloww ↓

4(x+2)+5x= 6(x+4)
4x+8=5x= 6x=24
9x+8= 6x+24
9x-6x+8= 6x-6x+24
3x+8= 24
3x+8-8= 24-8
3x=16
x=16/3

So she thinks it is 86 out of the 108, giving you a fraction of 86*100/108= 4300/54 or 79.6% which is how much she is correct and hence she is 100-79.6= 21.4% wrong.