Question $2$ to Question $5$ is based on this problem:

The Bon$-$BBQ Grill Company manufactures and sells four different types of grills: pellet, propane, electric and charcoal. The unit price and manufacturing cost for each type of grill are summarized as follows.

Table $1-1.$png

Each grill goes through four operations in the manufacturing process. The hours required by each type of grill in each of these manufacturing processes are summarized as follows.

Table $2-3.$png

In the next production cycle there are $2,400$ hours of machine press time available, $6,000$ hours of fabrication, $3,300$ hours of assembly, and $1,500$ hours of testing capacity. Bon$-$BBQ Grill can sell everything they make and wants to be sure that they produce at least three times as many electric grills as charcoal grills.

Formulate an LP model to maximize the profit.

Given the following decision variables:

X$1$: Number of pellet grills to produce

X$2$: Number of propane grills to produce

X$3$: Number of electric grills to produce

X$4$: Number of charcoal grills to produce

Which of the following represents the testing time availability constraint?