Concept:Use ratio cross-multiplication to find the relation between a and b, then evaluate the required ratio.Explanation:Given 6a2−ab2ab−b2=61.Cross‑multiplying: 6(2ab−b2)=1(6a2−ab).Expanding: 12ab−6b2=6a2−ab.Bring all terms to one side: 0=6a2−ab−12ab+6b2.Thus 6a2−13ab+6b2=0.Factorise: (2a−3b)(3a−2b)=0.So 2a−3b=0 or 3a−2b=0.Case 1: 2a=3b⇒a:b=3:2.Then (a+b):(a−b)=(3+2):(3−2)=5:1, i.e. value 5.Case 2: 3a=2b⇒a:b=2:3.Then (a+b):(a−b)=(2+3):(2−3)=5:(−1), i.e. value −5.Hence the required ratio equals 5 or −5.Answer:−5 or 5 (Option D).