linear programming

How on earth do you know how to draw inequalities such as x is less than or equal than 3y or 4y is greater than or equal to x???????

Eg $x \leq 3y \Rightarrow \frac{x}{3} \leq y$, so if you draw a graph of y = x/3 and shade the bits where
$\frac{x}{3} \leq y$ (test that using co-ordinates to find which side to shade.

In short, find an equation for y or find the x and y intercepts of something (eg 3x + 5y = 150), so the intercepts are x = 50 and y = 30 and draw a straight line between those two points.