Explanation:
Weight of the puppy at 4 weeks old:
pounds =
pounds
This weight is 3/5th times of the weight of puppy in 16 weeks. Let's assume the weight of puppy in 16 weeks be x. Then, 3/5th of x is 45/4 pounds.
In equation form,

Multiplying 5/3 both sides to isolate x on LHS,

pounds
The equation used for finding the weight of puppy is 3x/5 = 45/4. And Jayden's puppy weighed 18.75 pounds in 16 weeks.