In 2005, a nevada silver mine exported 200 tons of silver. in 2008, as the silver supply became exhausted, it only exported 25 tons of silver. what is the rate of change of the mine’s silver output?

To obtain the rate of change of mine's silver output, subtract the number of silver exported on 2005 from that on 2008. From the given, from 2005 to 2008, which is a span of 3 years, the exported silver decreased by 175 tons. Thus, the rate of change is equal to -175 tons per 3 years. 

D. i think it is the savings