Alright,
you will need to solve for each variable to find if they got the equation correctly or not..
Let's start with h
isolate h
(1/2)h = A/(b1+b2)
Now we need to get rid of 1/2 we may do so by multiplying both sides by 2
h = 2(A/(b1+b2))
And that's not how they did it for h so Option D doesn't apply
Let's see C
Also doesn't apply since they multiplied 2 only by A rather than A/h
Let's see B
Also not correct they made the same mistake as with option C
Let's see A
again same mistake
when multiplying both sides by 2
the 2 should be as following

I believe you should contact your instructor and explain that non of the options is right.
use a calculator instead of asking
A coefficient is a number multiplied by a variable.
In this case, our variable is a.
The coefficient is 12.
(PS: The +5 that isn't being multiplied by a variable is called a constant)
242mg
Explanation:
You would create a ratio for this situation
3oz/22mg=33oz/x
So we know 3*11=33 so we would do 22*11 and get 242 mg