For teh second one:
Let's treat 20 as one data point. There are 10 data points less than 20, and 20 data points more than 20.
In case you didn't know, the median is the middlemost number in a data set, when it is arranged from greatest to least.
For example, in the array (1, 3, 5, 7, 9), 5 is the median as it is in the middle. There are 2 numbers to its left, and 2 numbers on its right.
When dealing with arrays that don't have a middlemost number (i.e. having an even number of data points) like (1, 2, 3, 4, 5, 6), we just find the two numbers closest to the middle. Here, the medians would be 3 and 4.
Using this information, could you estimate in which interval the median for the plant set will be? I trust you can! :D