The average growth rate of oak is 0.3 m / year. in how many years will an oak grow 6 cm?

First, you need to convert the speed value from meters per year to centimeters per year.
To do this, multiply the speed value by 100 (in one meter, one hundred centimeters).
0.3m / year is equal to 30cm / year.
Now you need to divide 6cm by the growth rate.
6/30 = 0.2 year (or one-fifth of a year).
For convenience, you can find out in how many days a tree will grow.
365/5 = 73 (since there are 365 days in a year).
Answer: the tree will grow in 0.2 years or 73 days.