So when y = 2, t = 0. (Initial weight of puppy is 2 pounds)
So ln 2 = c.
So when t = 2, ln 3.5 = 2k + ln 2 (replace y (weight of puppy) with 3.5 pounds and t (2 months).)
So then ln 3.5 - ln 2 = 2k
k = [ln (3.5/2)]/2 = ...(hell if I know xD)
So when t = 3, ln y = 1.5*[ln(3.5/2)] + ln 2
So to find y at this point (for 3 months) all you have to do is let e^(RHS) = y.
And y should be 4.6 (approximately) ^^.