Find the minimum value of
[tex]\[ C = 6x + 7y \][/tex]
subject to the following constraints:
[tex]\[
\begin{cases}
4x + 3y \geq 24 \\
x + 3y \geq 15 \\
x \geq 0 \\
y \geq 0
\end{cases}
\][/tex]



Answer :

Certainly! To determine the minimum value of the cost function \( C = 6x + 7y \) subject to the constraints:

1. \( 4x + 3y \geq 24 \)
2. \( x + 3y \geq 15 \)
3. \( x \geq 0 \)
4. \( y \geq 0 \)

we follow these steps:

### Step 1: Convert Inequalities to Equalities

First, we need to convert the inequality constraints into system boundaries that we can graph or analyze.

1. \( 4x + 3y \geq 24 \) can be rewritten as \( 4x + 3y = 24 \).
2. \( x + 3y \geq 15 \) can be rewritten as \( x + 3y = 15 \).

### Step 2: Calculate Intersection Points

Now we find the points of intersection of the constraints \( 4x + 3y = 24 \) and \( x + 3y = 15 \), and also check boundaries \( x = 0 \) and \( y = 0 \).

Set up the equations as follows and solve them:

[tex]\[ \begin{cases} 4x + 3y = 24 \\ x + 3y = 15 \end{cases} \][/tex]

Subtract the second equation from the first one:

[tex]\[ (4x + 3y) - (x + 3y) = 24 - 15 \\ 3x = 9 \\ x = 3 \][/tex]

Substitute \( x = 3 \) into the second equation:

[tex]\[ 3 + 3y = 15 \\ 3y = 12 \\ y = 4 \][/tex]

So the intersection point of \( 4x + 3y = 24 \) and \( x + 3y = 15 \) is \( (3, 4) \).

### Step 3: Evaluate the Objective Function at the Vertex

We check this feasible point against the objective function \( C = 6x + 7y \):

[tex]\[ C = 6(3) + 7(4) \\ C = 18 + 28 \\ C = 46 \][/tex]

Thus, the minimum value of \( C = 46 \) occurs at \( x = 3 \) and \( y = 4 \).

### Final Answer

The minimum value of the cost function \( C = 6x + 7y \) subject to the given constraints is:

[tex]\[ C = 46 \][/tex]

with [tex]\( x = 3 \)[/tex] and [tex]\( y = 4 \)[/tex].

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