recall your d = rt, or distance = rate * time
notice, the time he took to cover 63 miles with the wind, is the same amount of time he took against it with 51 miles only, let's say, he took "t" hours long
and he was cycling at a rate of "r"
thus [tex]\bf \begin{array}{lccclll}
&distance&rate&time\\
&-----&-----&-----\\
\textit{with the wind}&63&r+2&t\\
\textit{against the wind}&51&r-2&t
\end{array}\\\\
-----------------------------\\\\
\begin{cases}
63=(r+2)t\implies \cfrac{63}{r+2}=\boxed{t}\\\\
51=(r-2)t\\
----------\\
51=(r-2)\left( \boxed{\cfrac{63}{r+2}} \right)
\end{cases}[/tex]
solve for "r"