To find the possible values of x when 4 is the highest common factor of 16 and x, we need to determine the factors of 16 and find the common factors with 4.The factors of 16 are: 1, 2, 4, 8, 16.The common factors of 16 and 4 are: 1 and 4.Therefore, the three possible values of x are: 4, 8, and 16.