Help with this cooling question

An apple pie comes out of the over at 425 degrees(f) and is placed on a counter in a 68 degree(f) room to cool. In 30 minutes it has cooled to 195 degrees(f). According to Newton's Law of Cooling, how many additional minutes must pass before it cools to 100 degrees(f)?

dT/dt = -k * (T - T[a])

T = temperature
T[a] = ambient temperature

dT/dt = -k * (T - 68)
dT/ (T - 68) = -k * dt
ln|T - 68| = -kt + C
T - 68 = C * e^(-kt)
T = 68 + C * e^(-kt)

t = 0
T = 425

425 = 68 + C * e^(0)
425 - 68 = C * 1
357 = C

T = 68 + 357 * e^(-kt)

t = 30
T = 195

195 = 68 + 357 * e^(-k * 30)
127 = 357 * e^(-k * 30)
127 / 357 = e^(-k * 30)
ln(127 / 357) = -k * 30
(1/30) * ln(127 / 357) = -k

T = 68 + 357 * e^((1/30) * ln(127 / 357) * t)
T = 68 + 357 * (127/357)^(t/30)

T = 100

100 = 68 + 357 * (127/357)^(t/30)
32 = 357 * (127/357)^(t/30)
32/357 * (127/357)^(t/30)
ln(32/357) = (t/30) * ln(127/357)
30 * ln(32/357) / ln(127/357) = t

t = 70.011211563592976316285839135611

70 - 30 = 40

About another 40 minutes