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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#)