Apparently the Big10 is getting paid $350 million for that prime Saturday afternoon game with 4.8 million viewers.
So if the Saturday night game (or Friday night game) has "only" 1.6 million viewers - 67% less - it's presumably worth 67% less, so "only" worth maybe $118 million for the season.
But that $118 million slot, combined with at least one or two games earlier that day (or on Friday), is what gets you to $350 million for the conference and $35 million per team.