Rachel has 42 blank audio cassettes, all of which are either 60 or 90 minutes long. If Rachel has less than 57 hours total of blank tape, how many 90 minutes tapes does she have?

Rachel has 42 blank audio cassettes, all of which are either 60 or 90 minutes long. If Rachel has less than 57 hours total of blank tape, how many 90 minutes tapes does she have?

Can you please help me with this problem? Me and my dad worked on it for about 25 minutes today:) and we never got the answer they wanted. If you would like, I can show you the work that we did. Thanks!

If you get 1/4 of a point deducted from your score if you answer a question incorrectly, is it worth it at the last few minutes of your test to fill in all of the questions with the same letter?

Here is a question that might be simple, though I am stuck on it:)
If you get 1/4 of a point deducted from your score if you answer a question incorrectly, is it worth it at the last few minutes of your test to fill in all of the questions with the same letter because the chances are that 1/4 of them will be right (especially if you can deduct some of the obvious wrong answers)? They tell you not to guess, but to me it seems like it is worth a shot since you will probably get at least 1/4 right.