Correct Answer - Option 2 : 80

**Calculation:**

Let CP of the pen be P

CP of the book be B

According to question,

⇒ -0.05P + 0.15B = 7 ____(i)

Now, If he sells the pen at 5% gain and the book at 10% gain

⇒ 0.05P + 0.10B = 13 ____(ii)

Adding equation (i) and (ii) we get,

⇒ 0.25B = 20

⇒ B = 80

**∴ CP of book is 80.**