Of means multiplication
So

And then simplify the numerator ad denominator
=

And simplify the numerator and denominator again
=

And we are finally left with the answer which is
Answer:
The total number of ways are 168.
Step-by-step explanation:
Consider the provided information.
There are 7 junior and 3 senior coders in her group.
The first project can be written by any of the coders. The second project must be written by a senior person and the third project must be written by a junior person.
For second project we have 3 choices and for third project we have 7 choices.
Now there are 2 possible case:
Case I: If first and second coder is senior, then the total number of ways are:

Case II: If first and third coder is junior, then the total number of ways are:

Hence, the total number of ways are: 42+126=168
One will be c
and 2 will be b
Well, they are equivalent, but I'm not sure if that's exactly what you're asking. :)