This is in a simplified form
Other forms are
'~~~~~~~~~ The teaching bit ~~~~~~~~~~~~~~~
Method to derive
If you multiply by 1 you do not change the value or the way it looks.
If you multiply I but in the form of
So you can write
If seen as
I wonder if the question was not meant to be
This is more likely because there is a calculation involved.
However, it would not be 'solve' rather determine or evaluate.
This simplifies to