Answer:
If a puppy weighs 12lbs when they came home and gains 3lbs per week, it will take them 12/3=<<12/3=4>>4 weeks to weigh 84lbs.
Explanation:
To solve this problem, we need to use the formula for simple interest, which is: I = P x R x T, where I is the interest, P is the principal, R is the rate, and T is the time. In this case, the puppy's initial weight is the principal, the rate is the amount they gain per week, and the time is the number of weeks it takes them to reach 84lbs.
We can plug these values into the formula to find the number of weeks it takes the puppy to reach 84lbs. The formula would look like this: 84 = 12 x 3 x T. Solving for T, we get: T = 84 / (12 x 3) = 84 / 36 = 12 / 3 = 4. Therefore, it takes the puppy 4 weeks to reach 84lbs.