A+b=9i-8j+7k+(7i-9k)
=9i-8j+7k+7i-9k
=16i-8j-2k
9a+7b=9(9i-8j+7k)+7(7i-9k)
=81i-72j+63k+49i-63k
=130i-72j
|a|=| 9i-8j+7k |
|a-b|=|9i-8j+7k-(7i-9k)|
=|9i-8j+7k-7i+9k|
=|2i-8j+16k|
i hope this is helping
Answer: 3π
I don't see 3π in your answer choices, but I'm assuming the "3x" is supposed to be 3π.
Step-by-step explanation:
To convert from degrees to radians, you multiply by π/180.

since ΔQRS similar to ΔQRP, then
SR/QR = QR/PR
x/12 = 12/(3.5+x)
x(3.5+x) = 12²
x² + 3.5x = 144
x² + 3.5x - 144 = 0

approximately 10.38