The following is a conversation between Gabriel and Heather:
Gabriel: "I am thinking of two distinct single-digit numbers. Can you guess the sum of these two numbers?"
Heather: "No. Can you give me a clue?"
Gabriel: "The last digit of the product of the two numbers is your house number."
Heather: "Now I know the sum of the two numbers."
So, what is the sum of the two numbers?
Note: It is possible that the product of the two numbers is a single-digit.