[alexlearner]

I would like to make up two sets of similar sentences in different tenses.

(1a) Over the last five weeks, Joe has earned $5000.
(1b) Over the last five weeks, Joe has been earning $5000.
(1c) Over the last five weeks, Joe earned $5000.

(2a) Over the last six months, May has written ten essays.
(2b) Over the last six months, May has been writing ten essays.
(2c) Over the last six months, May wrote ten essays.

I am not sure what tense to use when relating it to "Over the last ...". Please explain my question. Thank you very much.