The quantity \(X\) is increasing exponentially with respect to time \(t\). The table above shows values of \(X\) for different values of \(t\). Find the value of \(X\) when \(t = 20\).
The quantity \(Y\) is decreasing exponentially with respect to time \(t\) where
$$Y = 80 \mathrm { e } ^ { - 0.02 t }$$
Find the value of \(t\) for which \(Y = 20\), giving your answer correct to 2 significant figures.
Find by differentiation the rate at which \(Y\) is decreasing when \(t = 30\), giving your answer correct to 2 significant figures.