TIFR PHD CS & SS 2014

A body at a temperature of 30 Celsius is immersed into a heat bath at 0 Celsius at time t = 0. The body starts cooling at a rate proportional to the temperature difference. Assuming that the heat bath does not change in temperature throughout the process, calculate the ratio of the time taken for the body to reach 1 Celsius divided by the time taken for the body to reach 5 Celsius.