What the cambium made

A table gives the xylem cells and the phloem cells that a cambium made in each of six years. You will find the xylem cells for each phloem cell in every year. You will find the share of all the cells that became xylem. Then you will find the years in which xylem was more than four times the phloem.

The idea. Each year the cambium cuts cells towards the pith and towards the bark. The inner cells become xylem, and the outer cells become phloem.

Your tasks.

1. Set ratios to the xylem cells divided by the phloem cells for each year, in order.
2. Set xylem_share to the per cent of all cells, over the six years, that became xylem.
3. Set heavy_years to the years in which the ratio was greater than $4$.