A CFL is accepted by a stack, means using push and pop operations only, the every string of language should be accepted. Can you accept the above language using stack only?
For string $aaabbb$, you can use a stack saying Push all a's, then Pop() for every b in input string. and if we find our stack empty after seeing all b's, we can say Yeah!! string got accepted.
Can you do something similar to this for $aaabbbccc$?