Low Income/Affordable Housing Incentives

Could someone explain to me the topic of low income/affordable housing incentives. I’ve read some information about this topic, but it wasn’t presented clearly. I also have a few questions regarding this type of investing:

  1. Who provides the capital for this type of investing?

  2. Generally, how much capital is contributed toward the purchase of these types of properties?

  3. Does the contributed capital from federal/municipal funding have to be repaid?