Answer:
d) produce more guidebooks, because the next guidebook produced increases profit by $5.
Step-by-step explanation:
A perfectly competitive industry is characterised by many buyers and sellers of homogenous goods and services. There are no barriers to entry or exit of firms. In the long run, firms earn zero economic profit.
Profit is maximised where marginal revenue/ price is equal to marginal cost.
In this question, marginal revenue ($35) is greater than marginal cost ($30), so, the firm isn't maximising profit and they should increase production.
A firm should shutdown when average variable cost is greater than price.
I hope my answer helps you