[tex]v_b-the\ speed\ of\ the\ boat\\v_c-the\ speed\ of\ the\ current\\\\v_b+v_c=\frac{210}{10}=21\ (mph)\\\\v_b-v_c=\frac{210}{70}=3\ (mph)\\\\ +\left\{\begin{array}{ccc}v_b+v_c=21\\v_b-v_c=3\end{array}\right\\-----------\\.\ \ \ \ \ \ 2v_b=24\ \ \ \ /:2\\.\ \ \ \ \ \ \ \ \ v_b=12\ (mph)\\\\12+v_c=21\\v_c=21-12\\v_c=9\ (mph)[/tex]
[tex]Answer:\\the\ speed\ of\ the\ both\ is\ 12mph\\the\ speed\ of\ the\ current\ is\ 9mph[/tex]
