Answer:
The number of hardback books in book sale  = 58
Step-by-step explanation:
Let the number of hardback books  = m
So, the number of paperback books = 3 ( number of Hardbacks) Â - 12
                               = 3 m - 12
⇒the number of paperback books  = 3 m -12
Now, total number of  paperback books  = 162
⇒ (3m -12)  = 162
or, 3m = 162 + 12
or, 3m  = 174   ⇒  m = 174 / 3
or, m = 58
Hence, the number of hardback books  = 58