A thermometer is taken from a room where the temperature is 25°C to the outdoors, where the temperature is

A thermometer is taken from a room where the temperature is 25°C to the outdoors, where the temperature is -11° C. After one minute the thermometer reads 7°C.

(a) What will the reading on the thermometer be after 4 more minutes?

(b) When will the thermometer read -10°C?

By Newton's Law of cooling
T(t) = S +(To-S)*e(-kt) where To = initial temperature at t = 0
7 = -11 + (25+11)*e^(-k)
18 = 36e^-k
ln(0.5) = -k
k = 0.693
T(t) = -11+36e^(-0.693t)
(a) T(5) = -11+36e^(-0.693*5)
T(5) = -9.9 C
(b)
-10 = -11+36e^(-0.693t)
1/36 = e^(-0.693t)
ln(1/36) = -0.693t
t = 5.17 minutes