Final answer:
The OCC's Regulation 12 CFR 9.10 requires that cash can be invested promptly, which means daily for most institutions.
Step-by-step explanation:
The OCC's Regulation 12 CFR 9.10 requires that cash can be invested (made productive) promptly, which means daily for most institutions. This means that banks are required to invest their cash reserves quickly and efficiently to generate returns. The regulation does not specify a minimum balance to invest or exclude income cash from being invested.