-69 A = -6 then A-1 =

I need help and answer key for 14 and 15

I have this question on my homework and I don't see a pattern. I have to explain how the trick works.  "Think of a number. Add 17. Double the result. Subtract 4. Double the result. Add 20. Divide by 4. Subtract 20. Your answer will be your original number."

The average A of three numbers a1, a2, a3.

Table continues in second photo! Thank you!

Please answer both questions and be detailed, thank you in advance!

Simplify. V48 + V75 + V12 = %3D Submit Question

A student needs to answer 20 out of 30 questions on a test. Find the number of ways the student can choose if the student must answer the first 8 questions on the test.

I only need the answer for the one marked in yellow, what did I do wrong and what is the correct answer? Thank you.