Exp. (a)
Given, X has 7 friends, 4 of them are ladies and 3 are men while Y has 7 friends, 3 of them are ladies and 4 are men.
∴ Total number of required ways
=3C3​×4C0​×4C0​×3C3​+3C2​×4C1​×4C1​×3C2​
+3C1​×4C2​×4C2​×3C1​+3C0​×4C3​×4C3​×3C0​
=1+144+324+16=485