Setting up linear equations.

In a practise GCSE mock exam paper i saw these 3 questions and i think i have got the right answers but i wondered if you could just check for me.

1. A girl is Y years old. Her father is 23 years older than she is. The sum of their ages is 37. How old is the girl?

So i did this:

Y + 23 = 37

37 - 23 = 14

2. A boy is X years old. His sister is twice as old as he is. The sum of their ages is 24. How old is the boy?

So i did this:

X times X = 24

24 divided by 2 = 12

3. On a bookshelf there are 2b crime novels, 3b - 2 science fiction novels and b + 7 romance novels. Find how many of each type of book there is, if there are 65 books altogether.

So i did this:

2b + 3b - 2 + b + 7 = 65

then i simplified it: 6b - 9 = 65

i then added 9 to both of the whole numbers so i now have:

6b = 74

And then i divided each side by 6.

So i now have b = 12.5

so.. Crime novels = 2 x 23.5 = 25

Science fiction novels: 3 x 12.5 = 37.5 and then i - 2 which equals 35.5

Romance novels: 12.5 + 7 = 19.5

Please can you tell me if i've gone wrong in any of these problems.

Thanks in advance :)