[Yaybob]

A)
9*8 = 72

B) 3! + 5!
= 3*2*1 + 5*4*3*2*1
= 6 +120
=126

C)
P (n,r) = n! / (n-r)!
P (4, 4) = 4!/(4-4)!
= 4!/0!
= 4!/1!
= 4*3*2*1
= 24

D)
C (n,k) = n! / [k!(n-k)!]
C (5, 3) = 5!/3!2!
C (5, 2) = 5!/2!3!
C (5, 3) / C (5, 2) = 1