Answer:
Original number is 47
Step-by-step explanation:
Given: The tens digit is three less than the units digit. If the digits are reversed, the sum of the reversed number and the original number is 121.
To find: the original number
Solution:
Let x denotes digit at ones place.
As the tens digit is three less than the units digit,
Digit at tens place = 
Original number = 
When digits are reversed,
Reversed number = 
As the sum of the reversed number and the original number is 121,

So,
original number = 