Each letter in the addition sentence AA+BB+CC=BAC.What are the values of A,B and c?

In the result of the sum, BAC, there is a C in the units position. This tells us that
A + B + C = 1C and
A + B = 10

Well, AA, BB etc. means simply A(10^1 + 10^0) = A * 11, ...
(A + B) * 11 = 110.

Only if C were to be 9, B could be 2:
110 + 99 = 209

But, as A + B = 10, A cannot be 0 (Look at the Tens position in the result BAC).
Hence
B = 1 and
A = 9.

Finally, subtract the 1 in the tens position of 110 from A to obtain C:
C = 9 - 1 = 8.

So the answer is:

AA + BB + CC = BAC -> 99 + 11 + 88 = 198.