For the next 20 years, W is measured in tons, T is measured in years from the start of 2010. All right, let's get into this. So part A, use the tangent line to the graph of W at T equals zero to approximate the amount of solid waste that the landfill contains at the end of the first three months of 2010. So since time is in years, that would be three months would be 1 4th of a year, so T equals 1 4th. So it seems at first it's really daunting, they gave us a differential equation, we don't even know what W, what the actual function W is, how do we figure out its tangent line, but we just have to kind of think about what they're asking. So regardless of what W looks like, so let's think about it a little bit. So we don't know yet what W actually does look like, but they tell us it's an increasing function.