A publisher sells either digital copies of their new book, paperback copies or hardback copies. For every 4 digital sales they make, they make 5 paperback sales and 1 hardback sale. In the first week of sales, the company sells 308 more paperback copies of the book than hardback copies.

This means in the first week the number sells of digital copies is 308, paperback sells was 385 copies and hardback sell was 77 copies

Step-by-step explanation:

Let the number of digital copies be x, the number of paperback copies be y and the number of hardback copies be z.

4 digital sales is equal to 5 paperback sales and 1 hardback sale.

5x = 4y, x = 4z, y = 5z

The company sells 308 more paperback copies of the book than hardback copies

y = 308 + z

But y = 5z

5z = 308 + z

4z = 308

z = 77

y = 5z = 5(77) = 385

x = 4z = 4(77) = 308

This means in the first week the number sells of digital copies is 308, paperback sells was 385 copies and hardback sell was 77 copies