Answer:
The mean is 280 customers.
The sample proportion is 28%.
Explanation:
For each customer, there are only two possible outcomes. Either they plant a vegetable in the spring, or they do not. This means that we can solve this problem using concepts of the binomial probability distribution.
Binomial probability distribution.
Probability of exactly x sucesses on n repeated trials, with p probability. Has an expected value of:

In this problem, we have that:
There are 1000 customers, so
.
28% of its customers plant a vegetable garden in the spring. This means that
.
So:
What is the mean of the sampling distribution of modifyingabove p with caretp?
The mean is the expected value, so:

The mean is 280 customers.
The sample proportion of customers that plant a vegetable garden in the? spring?
It is the same as the population proportion, so the sample proportion is 28%.