The equation that can be used to represent the weight of the dog when he was 6 months old is 64/x.
The equation that can be used to represent the dog's current weight is: 64 = 3x
Where x represents the weight of the dog when he was 6 months old
In order to determine the value of x, divide both sides of the equation by 3
x = 64/x
To learn more about division, please check: https://brainly.com/question/13281206