The quantity of a substance can be modeled by the function A(t)A(t) that satisfies the differential equation \frac{dA}{dt}=-\frac{1}{80}(A-400). dt
dA
​
=−
80
1
​
(A−400). One point on this function is A(1)=720.A(1)=720. Based on this model, use a linear approximation to the graph of AA at t=1t=1 to estimate the quantity of the substance at t=0.8.t=0.8.