The difference between a two-digit number and the number obtained by interchanging the positions of its digits is 45. What is the difference between the two digits of that number?
Choose the correct choice from the following options:
A) 4  B) 5  C) 6  D) 8  E) 9

Rationale: "sol . let the ten ’ s digit be x and unit ’ s digit be y , then , ( 10 x + y ) - ( 10 y + x ) = 45 ⇔ 9 ( x - y ) = 45 ⇔ x - y = 5 answer b"
Answer: B