We have written thisese pages this afternoon. We have written these pages this afternoon.

"This" is singular. "These" is plural.

I put this sentence in present perfect, becuause I wriote since this morning until this aternoon. I put this sentence in present perfect because I wrote since this morning.

If you use "since", it's implied that you want to specify the start of a certain action. However, if you want to specify a duration of time, you can use "from" and "to". For example, "from morning to the afternoon.

I put this sentence in present perfect, because I'm no. I didn't do my homework there was many days until yetbecause there is a lot of days until the deadline. I put this sentence in present perfect. I didn't do my homework because there is a lot of days until the deadline.