Sophie's favorite number is a two-digit number. If she reverses the digits, the result is 36 less than her favorite number. Also, one digit is 3 more than double the other digit. What is Sophie's favorite number?
[10a + b] - [10b + a] ==36
a =2*b + 3, solve for a, b
a==5 and b ==1
Sophie's favorite number ==51
