Application Of Derivatives

A body at an unknown temperature is placed in a room which is held at a constant temperature of \(30^{\circ} \mathrm{F}\). If after 10 minutes the temperature of the body is \(0^{\circ} \mathrm{F}\) and after 20 minutes the temperature of the body is \(15^{\circ} \mathrm{F}\), then the expression for the temperature of the body at any time \(\mathrm{t}\) is