Your equation is a linear equation and it was entered in standard form, hence there is no manipulation possible when solving for 'y'. 

For two variables, two equations are required in order to solve for specific values.  If you wished to solve for 'x' rather than 'y' then the solver will manipulation the equation to solve for 'x' if that variable has been chosen (that example is shown in the second image). 

For any graphable equation, the software first manipulates it into its standard form before graphing; for a linear equation, that form is "y=mx+b" where the slope "m" may then be determined by inspecting the equation (for example, in the equation "y=-2x+4" "-2" is the correct value for "m"). For a parabolic equation, the standard form is y = a(x - h)^2 + k, from which direction (polarity of "a") and axis of symmetry (value of "h"), etc. may be determined by inspection.