Yahoo Inc’s board of directors on Friday is in the third and final day of meetings that could decide the future of one of Silicon Valley’s most prominent but troubled companies. One option on the table for the nine board members is whether to sell Yahoo’s core business, which includes Mail, its sports sites, and advertising technology. The company is also in the process of deciding whether to continue with the spinoff of its $30 billion stake in Chinese e-commerce company Alibaba Group Holdings Ltd.