How do I know if my husband meets the minimum income requirements for the I-864?

My husband has a good job, we can afford to pay for our own house (rent), food... He is the main petitioner, and I am the immigrant. We submitted form I-864 with him as the petitioner and, just in case, his mom as a joint sponsor -with any doubt, she meets the requirements-. We got a Request for Initial Evidence, saying that my husband doesn't meet the requirements. I checked and double checked and he does, or so I think. How can I know for sure that he does meet those requirements? His annual income is above 30000/year. Thanks a lot