The Bill & Melinda Gates Foundation will spend $100 million over five years to fund a group of nonprofit organizations working to help colleges “transform themselves” in the face of falling enrollment, increasing demands for educated workers and declining public confidence in higher education, it said Thursday. That means overhauling colleges’ business models, structures and cultures to boost student outcomes, which can be measured by metrics like graduation rates and successful transfers from community colleges to four-year institutions. The foundation also wants the effort to help institutions address stubborn equity gaps so race, ethnicity, family income and other demographics don’t predict whether a student is likely to graduate from college.