Explanation:
6A = B
100+A = C
A + B + C = 692
just replace B and C with A values
A + (6A) + (100 + A) = 692
8A = 592
A = 74
take A and put back into original relationships to find other numbers.
6A = B
6(74) = 444
100 + A = C
100 + (74) = 174
74 + 444 + 174 = 692