ab has a value in the decimal system as:
10a+b
This number reversed has a value of 10b+a and we are told that this value is 27 more than the original so
10b+a+27=10a+b
9b-9a+27=0
9b-9a=-27
b-a=-3
a=b+3 and we are also told that a+b=11, b=11-a so
a=11-a+3
2a=14
a=7 and b=4
So the original number was 47
check...
74-47=27
and
7+4=11
