The number of fruit flies in a kitchen triples every day. After 4 days, there are 81 fruit flies.
Which equation models the number of fruit flies after x days pass?
A. 27x=81
B. 3* = 81
C. 4* = 81
D. 3x = 81
E. 4x = 81

The answer is E. 4x=81

It's just not realistic to present a list of 12 math questions and ask for the answers to all of them at once.  Please post only one question at a time and please share your thoughts about how to solve that question.

I'll focus on one problem:    7 2/3 + 2 7/12

Here the LCD (lowest common denominator) is 12.  7 2/3 becomes 7 8/12.

Add 7 8/12 and 2 7/12:

 7 8/12
+2 7/12

9 15/12                15/12 is not a proper fraction.  Write it as 1 3/12, or 1 1/4.

Then your 9 15/12 becomes (9+1)  1/4, or 10 1/4.