heat transfer question but do nkt solve the problem I aant to undestand how you get 2h

i need to know how you get 2h from this problem. i know it has to be use the coolant law

The free convection heat transfer coefficient on a thin hot vertical plate suspended in still air can be determined from observations of the change in plate temperature with time as it cools. Assuming the plate is isothermal and radiation exchange with its surroundings is negligible, evaluate the convection coefficient at the instant of time when the plate temperature is 245C and the change in plate temperature with time (dT/dt) is 0.028K/s. The ambient air temperature is 25C and the plate measures 0.40.4m with a mass of 4.25kg and a specific heat of 2770J/kgK