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.
Thomas Eliot works multiple themes in the poem, however in general, his usage of imagery mainly represents ageing and decay. In the lines "When the evening is spread out against the sky / Like a patient etherized upon a table", the phrases like "sawdust restaurants" and "cheap hotels," the yellow fog, and the afternoon "Asleep...tired... or it malingers", represent decay. The character's concerns about his hair and teeth which is mentioned in the lines "Combing the white hair of the waves blown back / When the wind blows the water white and black," show the problems about aging.
If you've actually read the short story, you'll notice that when The Misfit starts to explain his father's death that tension levels are raised up.
