Answer:
(a) It will take Jones 25 hours to produce a finished book of 150 pages
(b) The marginal cost of the 150th page of the finished book is $4
The marginal cost of the 300th page of the finished book is $8
Explanation:
q=
= 
q = the number of pages in the finished book
S = the number of working hours spent by Smith
J = the number of hours spent working by Jones.
For first draft, smith works for 900 hours at $3 per working hour
q = 
q=
× 
q = 30 × 
=
, squaring both sides we have,
(
)² = J
(a) Since Jones has to produce a book of 150 pages and Smith worked 900 hours on it,
q = 150, S = 900 , J = ?
J = (
)² = 5²
J = 25
Therefore, it would take 25 hours for Jones to produce a book of 150 pages.
(b) (
)² = J
Since Smith worked for 900 hours at $3 per working hour, his total cost of work is = 900 × $3 = $2,700.
Jones total cost of work at $12 per working hour = $12J
Total cost of work, C = $2,700 + $12J
C = $2,700 + $12(
)²
Marginal cost, MC = 
=
[$2,700 + $12(
)²]
= 
if q = 150, MC = 
= $4
if q = 300, MC =
= $8