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Answer 1 · 2018-03-11T18:39:24

$A. 4/3$

Given, $L prop 1/d^2$

so, $L=k/d^2$ where, $k$ is a constant

Given, $L=12$ for , $d=3$

so,we can write,

$12=k/3^2$

or, $k=12*9$

Now,if intensity is $L'$ when the distnace $d'$ is $9m$ ,we can write,

$L'=k/9^2=(12*9)/(9*9)=4/3$ (as, $k=12*9$ )