we have the formula
step 1
Find out the value of k
we have
T=150 degrees
Ts=70
To=200
Do=200-70=130
t=10 min
substitute
Apply ln on both sides
substitute the value of k in the given formula
Now
For t=20 min
Ts=70
To=200
Do=200-70=130
substitute
The answer is option A