I have this problem I can't solve.
After having been shaped by heat, a piece of metal with temperature of 1500 degrees Celsius must be dropped into a tank of water to cool. The tank of water is kept at a temperature of 35 degrees Celsius after 10 min in the cooling tank, the metals temperature temperature drops to 750 degree Celsius. The rate of decrease in the metals temperature is said to be negligible when the metal reaches 75 degree Celsius, so the metal is removed from the tank when it reaches this temperature.
to the nearest hundredth, what is the negligible rate of temperature. eqaution is T-Ts = (TO - Ts) ^ekt

Question

I have this problem I can't solve. 
After having been shaped by heat, a piece of metal with temperature of 1500 degrees Celsius must be dropped into a tank of water to cool. The tank of water is kept at a temperature of 35 degrees Celsius after 10 min in the cooling tank, the metals temperature temperature drops to 750 degree Celsius. The rate of decrease in the metals temperature is said to be negligible when the metal reaches 75 degree Celsius, so the metal is removed from the tank when it reaches this temperature. 
to the nearest hundredth, what is the negligible rate of temperature. eqaution is T-Ts = (TO - Ts) ^ekt