I ____ (read) six books this week.
The correct answer is:
I have read six books this week.
Why are we using Present Perfect since we specify when we did the activity? Is it wrong to say (Past Simple):
I read six books this week.
Present perfect is the more likely answer, but both choices are possible, depending on whether you view 'this week' as incomplete (>present perfect) or complete (>past simple), which in turn depends on when in the week you say this.
Use the Present Perfect tense if something happened during an unfinished time period, such as "today," and there is a possibility it might happen again before the time period is over.
Reporter talking about a hostage situation:
Back to your question, I'd say "I have read six books this week" if there is the possibility that I might read more books before the week is over and "I read six books this week" if there is not.