They can change the background or the set up of the play to change the mood
If "y" represents the monthly salary of a salesman then we can rearrange the equation so that "y" is in evidence:
y=2000+100x
If he sells no computers and "x" is the number of computer systems he sells, then x=0.
y=2000+100*0 <=> y=2000+0 <=> y=2000
If the salesman sells no computers, his monthly salary is of 2000.
