The ratio of elements in a compound

Three laboratories make copper oxide and weigh the copper and the oxygen in their samples: $4.0\ \text{g}$ and $1.0\ \text{g}$; $6.4\ \text{g}$ and $1.6\ \text{g}$; $10.0\ \text{g}$ and $2.5\ \text{g}$. You will make the program find the ratio of copper to oxygen in each, their average, and the mass of copper in $50\ \text{g}$ of the oxide. Then it draws copper against oxygen.

The idea. A compound always has its elements in the same ratio by mass (the law of constant proportions), so the points lie on one straight line through the origin.

Your tasks.

1. Inside the loop, work out r, the mass of copper divided by the mass of oxygen.
2. Find average, the average of the three ratios.
3. Find copper50, the copper in $50\ \text{g}$ of the oxide: a share of $\dfrac{r}{r + 1}$ of it.