Which system can be used to represent, x the number of tetra fish, and y, the number of goldfish, he purchased?

The equation that would best describe the situation would be the first option. To solve this question, simply break down the question into sections and then use variables X and y to represent each of the things asked for in the problem. We know the following:

X = no of tetra fish
Y = no of goldfish
If there is twice as much goldfish than tetra fish, then it would be 2y.

X = 2Y.

Then knowing what X and y represent, find the equation that gives the total cost of fish he bought, knowing that 1.50 is for a goldfish and 2.00 is for a tetra fish.

12.

13.

16. is already in simplest form.