Let the hundredth digit of this three-digit number be A, the tenth digit be B and the unit digit be C, then this three-digit number is (100a+ 10b+c).
a+b+c= 12
b-c=2
100 a+ 10 b+c-( 100 c+ 10 b+a)= 99
So, a=4, b=5 and c=3.
This three-digit number is 453.