Question 732463
Going upstream, the speed along the riverbank
is {{{ 9 - 2 = 7 }}} m/s
Going downstream, the speed along the riverbank 
is {{{ 9 + 2 = 11 }}} m/s
The boat should travel at angle {{{ a }}},
( heading against the current )
so that {{{ sin(a) = 2/9 }}}
This is {{{ 9 }}} m/s at angle {{{ a }}}, and
{{{ 2 }}} m/s will bring the boat straight across.
You can find {{{ a }}}