Let S denote Smith's earnings, and let J denote Jack's earnings.

QA is therefore S, and QB is 2J.
We know from stem that S=20,000+J
QA can be written as 20,000+J
Notice that J is common to QB and QA, so subtract it out.
Now QA is 20,000 and QB is J.

Notice that the stem also tells us that Smith's compensation is less than 40,000.
So we know that 20,000+J<40,0000
J<20,000
The above answers our questions, telling us that QA must be greater.

A.