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.