Solution:
Let's denote Smita's present age as x. According to the problem, Smita's mother's present age is 3 times Smita's age, so we can express it as 3x.

After 10 years, Smita's age will be x + 10, and her mother's age will be 3x + 10.
3x + 10 = 2(x + 10)
3x + 10 = 2x + 20
3x - 2x = 20 - 10
x = 10

Therefore, Smita's present age is 10, and her mother's present age is 3 times that, which is 3 * 10 = 30.

Solution:
Let's assume the two-digit number to be represented as 10a + b, where 'a' represents the tens digit and 'b' represents the units digit.

a + b = 12
10a + b = 10b + a + 36
10a - a = 10b - b + 36
9a = 9b + 36
a = b + 4
b + 4 + b = 12
2b + 4 = 12
2b = 12 - 4
2b = 8
b = 4

a + 4 = 12
a = 12 - 4
a = 8

Therefore, the tens digit 'a' is 8, and the units digit 'b' is 4. So, the two-digit number is 84.