Answer: 405,000 paperback copies were sold
Step-by-step explanation: Before the paperback version of the novel was issued for sale, there were 36000 copies of the hardback copies available.
From the time the "first paperback..." version was issued and sold out, there nine times as many paperback copies as hardback copies that were sold. That is, during the period in question, for every hardback, there was an equivalent of nine paper back.
If paperback is p, and hardback is h, what we have in effect is;
Total = p + h
However, based on the information given, 1h equals 9p. If h equals 36000, then paperback equals;
9 x 36000 = 324000
Up till the last copy of the novel was sold (441000 copies were sold), 36000 hardback copies were sold and an initial 324000 paperback were also sold.
If the total units sold was given as 441000, then the equation becomes
Total = p + h + x
Where x is the extra units sold that gave rise to the total sales
441000 = 324000 + 36000 +x
441000 =360000 + x
Subtract 360000 from both sides of the equation
81000 = x
Therefore the total paperback copies that were sold is given as
324000 + 81000 = 405,000
