let x = tens digit of the original number

y = units digit of the original number

so, original number has the value (10x + y)

When the digits of a two-digit number are reversed, the new number is 9 more than the original number ...

digits reversed (the new number) ... 10y + x

the new number is 9 more than the original number ...

10y + x = 9 + (10x + y)

sum of the digits of the original number is 11 ...

x + y = 11

you should be able to solve the problem using the last two equations.