Chris' still water speed is 3mph, and the current's is 1.5mph... well, when Chris is going upstream, he's really not going at 3mph, since is not still water, the water is actually running, so, he's going " 3 - 1.5 " mph.
now, recall you d = rt, distance = rate * time
[tex]\bf \begin{cases}
d=1.2\\
r=3-1.5=1.5
\end{cases}\implies d=rt \implies 1.2=1.5t\implies \cfrac{1.2}{1.5}=t
\\\\\\
0.8=t\impliedby \textit{0.8 hours or 48 minutes}[/tex]
