I'm really stuck on this problem. Can anyone help?

You are given the 4 x 4 grid below.

(a) Find the number of ways of placing 8 counters in the squares (at most one counter per square), so that each row contains exactly two counters.

(b) Find the number of ways of placing 12 counters in the squares (at most one counter per square), so that each column contains exactly three counters.

sandwich Feb 15, 2023