In the function showing the cost for any number of apples, what is the input or x-value

What is the missing step in this proof ?

The standard deviation for a set of data is 5.5. the mean is 265. what is the margin of error?

The input to the function is x and the output is y. write the function such that x can be a vector (use element-by-element operations). a) use the function to calculate y(-1.5) and y(5). b) use the function to make a plot of the function y(x) for -2 ≤ x ≤ 6.