Final answer:
The equation that represents the total number of goldfish in the fish tank is y = 4x.
Step-by-step explanation:
To represent the total number of goldfish, y, in the fish tank, we need to consider that there are 4 times as many goldfish as black mollies. Let's assume that the number of black mollies is x.
Therefore, the number of goldfish would be 4 times x, or 4x. The equation that represents the total number of goldfish would be y = 4x.