I believe it is the Odometer
This is a geometric sequence with a common ratio of 2
an = a1 * r^(n - 1)
n = term to find = 21
a1 = first term = 0.05
r = common ratio = 2
now we sub
a21 = 0.05 * 2^(21 - 1)
a21 = 0.05 * 2^20
a21 = 0.05 * 1048576
a21 = 52428.80 <==== after working 21 days
Answer
According to newton law of cooling
and
now At Ta = 100
T₀ = 10 °C
T₁ = 12° C
10 = C + 100
C = -90
now,
at time equal to t
T(t) = 70
t = 48.88 s
hence, after 48.88 s the temperature of the body will be 70°C
b) time taken to reach 98°C
t = 390 s
hence, after 390 s the temperature of the body will be 98°C
2^2+b^2=12^2
4+b^2=144
144-4=140
√140 = √b
11.83 = b