Techniques For Solving Equations and Inequalities

Okay, so im facing a little difficulty with some of this, for example:

So you have to make LS=RS using trial and error. Now thats all find and dandy except that the answer is 2.5. For this, one side is positive the other is negative...

Another question is for the x must be between o and pi, does that mean I can only use numbers between 0 and 3.14 or is that some sort of radian measure?

The answer is -2.1???? Wouldn't -1 make much more sense?

Im probably missing something simple here, but im going crazy nonetheless.