Probability you'd pick an odd number:
1 2 3 4 5 6 7 8
Odd numbers: 1 3 5 7
There are 4/8 odd numbers so probability is 4/8 first pick.
Card is put back so you still have 8 cards. Probability greater than 6:
7 and 8 are greater than 6, so that's 2 out of 8 cards. Probability: 2/8
Multiply both probabilities together: 4/8 x 2/8 = 8/64 = 1/8