4th grade math please help!

Question

In Sean’s fish tank there are 6 times as many goldfish as guppies. There are 21 fish in the tank.

How many more goldfish are there than guppies

Answer 1

Let X be the number of goldfish and Y be the number of guppies and total number of fish is 21

Therefore X + Y = 21

but there are 6 times as many goldfish as there are guppies so X = 6Y

substituting for X gives

6Y + Y = 21

7Y = 21

Y = 3 which is the number of guppies

Since there are 6 times as many goldfish as guppies there are 6 x 3 = 18 goldfish

There are 15 (18 - 3) more goldfish than guppies

Answer 2

x represents the number of guppies

6x represents the number of godlfish

x + 6x = 21

Can you solve for x and answer?