Answer:
we have a number of two digits, ab.
The tens digit is a. the unit digit is b.
We know that:
a = 3 + b
b = r.
We can replace the second equation in the first one, and get:
a = 3 + r.
Then we have that our number is:
(3 + r) for the tens digit, and r for the unit digit.
Now, remember that the maximum possible digit is 9.
then the maximum possible value of r comes from.
3 + r = 9
r = 9 - 3 = 6.
Then the possibles values of r are: 0, 1, 2, 3, 4, 5 and 6.
