To find the mean number of plants per house, we use the Direct Method.

First, we calculate the class mark ($x_i$) for each interval, which is the midpoint of the class. Then, we compute the product of frequency and class mark ($f_i x_i$).

Number of plants	Number of houses ($f_i$)	Class mark ($x_i$)	$f_i x_i$
0 - 2	1	1	1
2 - 4	2	3	6
4 - 6	1	5	5
6 - 8	5	7	35
8 - 10	6	9	54
10 - 12	2	11	22
12 - 14	3	13	39
Total	$Σ f_i = 20$		$Σ f_i x_i = 162$

Mean $= \frac{\sum f_i x_i}{\sum f_i} = \frac{162}{20} = 8.1$

Method Used: I used the Direct Method because the class sizes were small and the values of the class marks ($x_i$) were small integers. This made the calculation of $f_i x_i$ simple and manageable without needing to assume a mean or use the step-deviation method.