The formula [tex] \frac{dT}{dt}=k(T-Tm)[/math] where k is a constant of proportionality also holds when an object absorbs heat from the surrounding medium. If a small metal bar whose initial temperature is 20oC is dropped into a container of boiling water, how long will it take the bar to reach 90oC if it is known that its temperature increased 20oC in 1 second? ? How long will it take the bar to reach 98oC ?

i'm really clueless on how to solve this problem. can anyone help? tq