A hot body placed in a surrounding of temperature θ_0 conforms to...

The body cools down according to Newton's law of cooling and its temperature decreases until it reaches thermal equilibrium with the surroundings.

The minimum temperature the body can attain is the temperature of the surroundings, which is $\theta_0$.

The initial temperature of the body is $\theta_1$.

The maximum fall in temperature of the body is $\Delta \theta = \theta_1 - \theta_0$.

The maximum heat lost by the body is given by $Q = ms\Delta \theta$.

Substituting the value of $\Delta \theta$, we get $Q = ms(\theta_1 - \theta_0)$.