The average cost when producing x items is found by dividing the cost function, c(x), by the number of items, x. when is the average cost less than 100, given the cost function is c(x) = 10x + 360?

a.) (0,4)
b.) (-infinity, 0) u (4, infinity)
c.) (4, infinity)
d.) (-infinity, 0] u [4, infinity)