Draw the graph of 5x + 4y = 40. Find where it meets the two axes, and one more point as a check.

Step 1. The x-axis. Put $y = 0$: $5x = 40$, so $x = 8$. The point is $(8, 0)$.

Step 2. The y-axis. Put $x = 0$: $4y = 40$, so $y = 10$. The point is $(0, 10)$.

Step 3. A check. Put $x = 4$: $20 + 4y = 40$, so $y = 5$. The point $(4, 5)$ must lie on the line through the first two.