Ah — likely mistake: 3:7 implies B is 7/10 = 70%, but 7:5 is 5/12 ≈ 41.7% — less. But if pre-industrial was 3:7 = 7 parts B, and modern is 7:5 = 5 parts B, then B decreased. But the question says how many more — so perhaps the ratio article is reversed? - go-checkin.com