Can you replace the question mark with the correct number?

Can you solve the below tricky visual equation?

How much will a 38° angle measure when looked at under a microscope that magnifies ten times?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.

John killed hundreds of people mercilessly and yet the police were not able to put her behind the bars. Why?

Considering the below equation:

V + II - VI = 10
IV - X + VIII = 20
IV - VII + VI = 30

Then, I + II + III = ?

Can you find out which number multiplied by itself will give the output as 12345678987654321?

Which five letter word can be added at the end of below word to form a
valid word?

> Pin
> Check
> Boiling
> View

It is always ahead of me yet I can never see it. What is it?

A boy purchased a book from a bookkeeper and gave him $100.
The cost of the book is $50 but the bookkeeper has no change, so he gets the change from the next shop and returns the boy his $50.

After some time the next shopkeeper came with the $100 note and told the bookkeeper that the note was a fraud, so he took the money back.

How much loss did the bookkeeper face?