Explanation:

Total student= 39, boys : girls = 2:1,

hence no of boys= 2/3(39)= 26
num of girls= 1/3(39) = 13 ,

since radhika ranked 15 among 39 student from top
and ranked 8 among girls from bottom ,

this means 7 girls are below radhika,

rest 13-9= 5 girls are above her,

now from 14 toper 5 are girls hence 14-5=9 boys.
Number of boys below radhika are 26-9=17

Hence, option 2 is the correct answer.