The temperature of an ingot of silver is 60 degrees Celcius above room temperature right now. Twenty minutes ago it was 70 degrees Celcius above room temperature. How far above room temperature will the silver be 15 minutes from now?

I'm not too sure how to start this problem. I believe the temperatures in coordinate points are (0,60) and (-20,70) and that Newton's Law is used to solve this problem [Ce^(kt) + T] Any help is appreciated. Thanks!