To find A-C, We will find 2's compliment of C and them add it with A,

That will give us (A-C)

2's compliment of C=1's compliment of C+1

=10101010+1=10101011

A-C=10101011+00001111

=10111010

Now (A-C) U B is .OR. logic operation on (A-C) and B

10111010.OR . 00110011

The answer is = 10111011,

Whose decimal equivalent is 187.