The goal is to get the variable by itself. For 24 you would get rid of 26 by adding (you need to do the opposite; positives subtract negatives add). The answer would be x=2
That same principle is applied in 25. All you need to do is add 1/4 to get 4/4 or 1 whole.
In 26 you would get the variable by itself by dividing by the number next to the variable. So divide by 3 to get -9