(Sorry I could only answer part A) The Answer is 84 -w-
I don't quite understand the ten strategy, or what EXACTLY you're asking. But, what you can do is when you add a one digit number plus a nine, just change the nine to a ten and subtract one. It is very easy. So, 7+10 equals 17, subtract one and you get 16 which is 7+9. It is always one less than anything plus 10.
Salutations!
12

- 9

=
Then,
- 9

-

Next, our final answer:
=

= 2
Our decimal would be 2.916667
Hopefully This Helps!!!
Answer:
6
Step-by-step explanation:
The mode is the number which appears most often in a set of numbers in this case that would be 6 because it appears twice