[tex]\bf \begin{cases}
r=\textit{rate of the plane}\\
w=\textit{rate of the wind}\\
\end{cases}
\\\\
\begin{array}{ccccllll}
&distance&rate&time(hrs)\\
&\textendash\textendash\textendash\textendash\textendash\textendash&\textendash\textendash\textendash\textendash\textendash\textendash&\textendash\textendash\textendash\textendash\textendash\textendash\textendash\textendash\textendash\\
\textit{with wind}&630&r+w&1\frac{1}{2}\\
\textit{against wind}&1120&r-w&4
\end{array}
[/tex]
[tex]\bf thus \begin{cases}
630=(r+w)1\frac{1}{2}\to 630=(r+w)\frac{3}{2}
\\\\
1120=(r-w)4\\
--------------\\
630=(r+w)\frac{3}{2}\implies 630\cdot \frac{2}{3}=r+w\\
420=r+w\implies \boxed{420-w}=r\\
--------------\\
thus\\
--------------\\
1120=(r-w)4\implies 1120=4r-4w
\\\\
1120=4(\boxed{420-w})-4w
\end{cases}
[/tex]
solve for "w", to find the wind's speed rate,
so hmmm what's the plane's rate? well 420 - w = r :)
