Final answer:
Julius has three times as many stamps in his collection as Liam and Mario combined.
Step-by-step explanation:
To find the relationship between Julius and his friends' stamp collections, we need to determine the number of stamps Liam and Mario have combined. Let's say Liam has x stamps and Mario has y stamps. According to the question, Julius has three times as many stamps in his collection as Liam and Mario combined. This can be represented by the equation 3(x + y).
Therefore, the correct answer is d. Multiply, Add, Subtract, Divide.