Some very good information can be obtained by simply clicking on a solution step.  As explained in the image below, "like terms" are grouped together, so "-12-16" is equal to "-28".  The final solution solves for 'x' by adding "+21" to both sides of the equation and "-28+21=-7". 

You might also like to change the "number of steps" to a higher level, also shown below. 

Finally, there is no need to repeatedly submit questions.  We will respond questions as we are able to, this is not an instantaneous medium for answers. 

a bit more detail: