According to Newton’s Law of Cooling:

Here is the rate of fall of temperature is the constant depending on nature of surface and surrounding conditions, A is the area of cross-section of the body, T is the average Temperature of the body and T₀ is the surrounding temperature.
It can also be written in Celsius scale as

Where θ and θ₀ are the temperature of the body and surrounding in Celsius scale respectively , k is a constant.
First condition:
Temperature falls from 65° C to 60° C.
Which means 5°C falls in 5 minutes,
∴
θ = 62.5 ° C
Substituting we get,


Second Condition:
Temperature further falls from 60 °C to 55 °C.
∴ dθ= 5 °C.
θ =
Substituting value of -k,dθ and θ in the equation we get,


Here we can conclude that time required for the body to go from 60 ° C to 55° C will be,


Thus, option (c) is the correct option.