Answer:
I will do only 1 sum bru.h
In the 1st sum
the 1st no. can be in 9 ways
the 2nd no. can be in 10 ways
the 3rd no. can be in 10 ways
the 4th no. can be in 10 ways
total no. of ways = 9 × 10 × 10 × 10
= 90 × 100
= 9000 ways
2nd one..
the 1st letter can be written in 4 ways
the 2nd letter can be written in 4 ways
the 3rd letter can be written in 4 ways
the 4th letter can be written in 4 ways
Total no. of ways = 4 × 4 × 4 × 4
= 16 × 16
= 196 ways