I need a little help. The problem is as follows: A pendulum clock with a pendulum made of brass is designed to keep accurate time at 18 °C. If the clock operates at 0.0°C, what is the magnitude of its error, in seconds per hour (use a minus sign to indicate slowing down)? The linear expansion coefficient of brass is 19 x 10-6 /C°. I tried multiplying the change in temperature by the coefficient of brass, but that does not come out right. I also tried multiplying that answer by 3600 to get the seconds but that was not right either. What else is there to do?