So, two score is 40 and four dozen is 48.

OK. Let us start with some facts.

The three numbers are prime.

Each number is greater than two score.

That is, each number is greater than 40.

And each number is less than four dozens.

That is, each number is less than 48.

So each of the prime numbers is greater than 40 and less than 48.

Do you know the prime numbers that are greater than 40 and less than 48?

They are 41, 43 and 47, and their sum is 41+43+47=131.