Answer:
a) This expression is simply the average of both of their hours for a full year.
b) Honestly, I'm not sure, but mathematically, its , so the hours cancel out and you get the ratio of their yearly hours? Idek
c) a/12 would be the number of hours Arjun worked per month since there are 12 months in a year.
d) This one is a difference between Arjun's hourly wage to Beth's hourly wage. So, it represents how much more Arjun would have made (Arjun's hourly wage) in comparison to Beth, or vice versa (depending on who worked more hours).
c) Similar to a), this is an average of their yearly income.