If u are using i as a variable the answer would be i= 3.
I think you could times 4 and 5 to get 20
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.
Answer:
4.52 x 10^-7
Step-by-step explanation:
you have a very small number (numbers to right of decimal) so you're exponent will be negative.