How many different two-digit numbers greater than 50 can be formed from the digits 3,6,7, and 9 of repetition of digits is allowed?

First of all the repeated digits numbers are 66,77 and 99 Total 3

Numbers beginning with 6 Total 3 (63,67 and 69).

Numbers begin with 7 Total3

and begin with 9 Total 3.

answer is 12