The Arctic Sea ice extent, the area of sea covered by ice, grows over the winter months, typically from November to March. Let $F(t)$ be the Arctic Sea ice extent, in million of square kilometers, as a function of time, $t,$ in days since November 1,2014 . Then $F^{\prime}(t)=0.073$ on January $1,2015 .^{11}$
(a) Give the units of the $0.073,$ and interpret the number in practical terms.
(b) Estimate $\Delta F$ between January 1 and January $6,$ $2015 .$ Explain what this tells us about Arctic Sea ice.