Step-by-step explanation:
Since, r varies directly as s
[tex] \therefore \: r \: \: \alpha \: \: s \\ \therefore \: r = k s..(1) \: \\ (k = \: constant \: of \: proportionality ) \\ plug \: s = 10 \: and \: k = 4 \: in \: equation \: (1) \\ r = 4 \times 10 \\ \huge \red{ \boxed{ \therefore \: r =40}}[/tex]
