The first step, and the key to success, is picking out the question.
Will profit increase? We need to determine the profit for each of the two choices
to find out which is greater. The formula for profit *P* is given by

where *R* represents the total revenue, and *C* represents the total
cost.

From here the problem has been broken up into four smaller problems. Each of these problems can be solved by writing down what we know.

What is the monthly cost for 8-hour production?

What is the monthly revenue for 8-hour production? The monthly revenue depends
on three factors given in the problem. The production rate
*r* = 150 wagon/hr, the amount of production time during the
month *t*_{8} = (21 days)(8 hr/day) = 168 hr, and
the price per wagon *p*_{8} = $15/wagon.

Note that we represented the production rate with a simple symbol *r*, because the
production rate (in wagons per hour) doesn't depend on the level of production. On the
other hand, we used subscripted symbols *R*_{8}, *C*_{8},
*t*_{8}, and *p*_{8} because these all depend on the level of
production

What is the total monthly cost if production is increased by 3,000 wagons per month? To answer this, we need to determine how many additional hours of production are needed, since that's what determines our added cost. We need to produce 3,000 additional wagons at a rate of 150 wagon/hr. This will take an addtional time

Knowing the additional production time, we can determine the additional cost

The total cost if production is increased by 3,000 wagons is

What is the total monthly revenue if production is increased by 3,000 units per month? Let's first find the total production time

Then we can use our revenue formula to find

Now we can compare the profit in each case:

Now we can see that it does not make sense to lower the price and increase production, since profit would decrease.