Light travels through tanks filled with various substances. The indices of refraction of the substances n and the lengths of the tanks are given. Rank them in order of the time it takes light to traverse the tank, from greatest to smallest. 

(a) n = 5/4, length = 1 m; 

(b) n = 1, length = 4/5 m; 

(c) n = 1, length = 1 m; 

(d) n = 3/2, length = 1 m; 

(e) n = 3/2, length = 5/4 m; 

(f) n = 3/2, length = 4/5 m.