Less than five months after vaulting to a $1.6b valuation, Divvy, an expense reporting startup for small businesses, is in talks to be acquired. Bill.com, a cloud software-based platform that helps small and midsize businesses with back-office financial operations, is Divvy’s expected buyer. The companies may be planning to announce the deal as soon as this week, when Bill.com, which currently carries a market cap of about $12b, is scheduled to report first-quarter earnings.