Answer:
Option A is correct

Explanation:
Direct variation says that:
then;
the equation is in the form of
, where k is the constant of variation
As per the statement:
The number of milligrams of a certain medicine a veterinarian gives to a dog varies directly with the weight of the dog.
Here, w represents the weight and d represents the dosage
then ,by definition of direct variation we have;
.....[1]
It is also given that if the veterinarian gives a 30-pound dog 3/5 milligram of the medicine
⇒w = 30 pound and d = 3/5 milligram
Substitute in [1] we have;

Multiply both sides by 5 we have;

Divide both sides by 150 we have;

Simplify:

⇒

therefore, equation relates the weight, w, and the dosage, d is:
