This is easy if you don't fall into the trap of forgetting the information. There's a lot happening so start with what's most important:

"the number of boys was one larger than the number of girls" So, from 25 children,

13 boys and 12 girls.Now,

" 25 children went to the circus, 60% of whom liked the clowns" So,

15 children liked the clowns. Next,

"the number of boys who liked the clowns was three more than the number who didn't"

From earlier, total boys = 13

Hence liked clowns = 8

Didn't like = 5

Finally,

"how many girls did not like the clowns?"

Total children that liked - Total boys that liked = 15 - 8

Hence girls that liked the clowns = 7

So girls that

DID NOT like the clowns = Total girls - The ones that liked

12 - 7 = 5

A