Answer:

n + 3 cm

Step-by-step explanation:

Area = Length x Width = 8n² + 24n

Since Width = 8n:

Length x 8n = 8n² + 24n

We can factor out 8n from 8n² + 24n

Length x 8n = 8n(n + 3)

Divide both sides by 8n

Length = n + 3 cm :)