if varies directly as s and inversely as the square of u,and r=2 when s=18 and u=2,find r when u=3 and r=27

"r ∞ s/u∧2

r = ks/u∧2

2 = 18k/2∧2

2 = 18k/4

k = 4/9

when u = 3, r = 27, k = 4/9

r = (4/9 × 27) ÷ 4

r = 12/4

∴ r = 3"