Given the original cost of each book be ₹x.
Total cost =₹960 (Given)
∴‌‌ Number of books for 960=‌

960

x

If the cost per book was ₹8 less, (i.e., x−8 ) then
‌ Number of books ‌=‌

960

x−8

According to question,
‌

960

x−8

‌=‌

960

x

+4
‌

960

x−8

−‌

960

x

‌=4
960[‌

x−x+8

x(x−8)

]‌=4
‌

8

x2−8x

‌=‌

1

240

⇒‌‌x2−8x‌=1,920
⇒‌‌x2−8x−1,920‌=0
‌⇒x2−48x+40x−1,920=0
‌⇒x(x−48)+40(x−48)=0
‌⇒‌‌(x−48)(x+40)=0
‌x=48‌ or ‌x=−40
∵−40 is not possible.
Hence, the original cost of each book =₹48 .