Hello, freakyfrog!
Are you skimming through some book?
This is a Linear Programming problem.
If this is an assignment, you should have been taught the procedure.
A tray of corn muffins takes 4 c milk and 3 c wheat flour.
A tray of bran muffins takes 2 c of milk and 3 c of flour.
A baker has 16 c milk and 15 c wheat flower.
He makes $3 profit per tray of corn muffins and $2 profit of bran muffins.
How many trays of each type of muffin should the baker make to maximize his profit?
Let $\displaystyle x$ = number of trays of corn muffins, $\displaystyle x \geq 0$
Let $\displaystyle y$ = number of trays of bran muffins, $\displaystyle y \geq 0$
Place the information in a chart:
. . $\displaystyle \begin{array}{cccc}
& \text{milk} & \text{flour} & \text{Profit} \\ \hline
\text{corn }(x) & 4x & 3x & 3x \\
\text{bran }(y) & 2y & 3y & 2y \\ \hline
\text{Total} & 16 & 15 \end{array}$
We have: .$\displaystyle \begin{array}{cccccccc}4x + 2y & \leq & 16 & \Rightarrow & 2x + y & \leq & 8 & [1] \\
3x + 3y & \leq & 15 & \Rightarrow & x + y &\leq & 5 & [2] \end{array}$
[1] Graph the line: $\displaystyle 2x + y \:=\:8$
. . Intercepts: (4,0), (0,8)
. . Shade the region below the line.
[2] Graph the line: $\displaystyle x + y \:=\:5$
. . Intercepts: (5,0), (0,5)
. . Shade the region below the line.
The shaded region looks like this: Code:

8 *
*
 *
5 o *
:* *
:::**
:::::o
::::::**
::::::::* *
::::::::* *
  o     o  *  
4 5
We are concerned with only the vertices of the shaded region.
We see three of them: (0,0), (4,0), (0,5)
The fourth is the intersection of the two lines.
Solve the system and we get: (3,2)
Test these vertices in the profit function: .$\displaystyle P \:=\:3x+2y$
. . and see which one produces maximum profit.
. . $\displaystyle \begin{array}{cc} & \text{Profit} \\ \text{Vertex} & 3x+2y \\ \hline
(0,0) & 0 \\ (4,0) & 12 \\ (0,5) & 10 \\ {\color{blue}(3,2)} & {\color{blue}13} \end{array}$
For maximum profit, he should make 3 trays of corn muffins and 2 trays of bran muffins.