Part A
The domain of a function is the set of possible values for the independent variable x, we can express the domain in interval notation like this: [xmin, xmax] where "xmin" is the minimum value of x and "xmax" is the maximum value of x. In this case, x goes from 0 to 4, then the domain of this function is [0, 4], the range is also the set of possible values but for the dependent variable y, then it can be represented like this: [ymin, ymax], in this case, "ymin" equals 0 (the smaller possible value of x according to the table) and "ymax" equals 8, then the range of the function is [0, 8].
Part B
As mentioned, the domain represents the set of possible values for x, in this context, x is the number of large designs that you can apply to T-shirts, then the domain is the set of possible large designs that can be applied, any number out of this interval ([0, 4]) can't be included like x=5.
Part C
As you can see, we have a linear relationship between x and y, as x increases, y decreases, once that we have reached the value of 4 of large designs we have a corresponding 0 for the number of small designs, then you can't jump up to x=5 because you would have a negative value for the variable "y".