(a) from the question, we can see
Sam has 20 more marbles than Kenneth
&
Sam has 8 more marbles than Raymond.

So,
Sam marbles
Kenneth : 20 less than Sam
Raymond : 8 less than Sam

As we can see, Kenneth would have 12 less marbles than Raymond. And Raymond have 12 more marbles than Kenneth.

(b)
Ratio of Kenneth : Raymond
5. : 7

Think of Kenneth having 5 packages with marbles and Raymond having 7 packages with marbles

Raymond has 2 more packages than Kenneth and
Raymond has 12 more marbles than Kenneth

So 1 package of marbles would be = 6
And Raymond has 7 packages.
So Raymond has 7x6=42 marbles