Please read the directions on the I-864 carefully, all the information is there.
On page 9 of the form:
What If I Cannot Meet the Income Requirements?
If your income alone is not sufficient to meet the requirement for your household size, the intending immigrant will be ineligible for an immigrant visa or adjustment of status, unless the requirement can be met using any combination of the following:
....
Income from the intending immigrant, if that income will continue from the same source after immigration, and if the intending immigrant is currently living in your residence. If the intending immigrant is your spouse, his or her income can be counted regardless of current residence, but it must continue from the same source after he or she becomes a lawful permanent resident.