Translation:How are you?
Hamjambo? is the short form of Hamna jambo? Where in this context jambo = problem.
Hamna jambo? = Don't you have a problem?
Remember how to get hamna from plural you.
You = Ninyi m; have = na; problem (jambo)
The negative is made by fixing ha before Subject marker 'm'
Ninyi 'ha'-m-na jambo. You do not have problem.
Ninyi ha-m-na- jambo? = Don't you have a problem?
How are you is not direct translation but just a hint.