Question 997437
This form of question is so common, it will be solved here only symbolically.


<pre>
KNOWN VARIABLES
{{{system(n=distanceUpStream,p=distanceDownStream,t=timeEachWay)}}}
UNKNOWN VARIABLES
{{{system(r=boatSpeed,c=speedOfCurrent)}}}

VARIABLES' ASSIGMENTS
{{{system(n=130,p=270,t=5)}}}

                speed        time       distance
UPSTREAM        r-c           t          n
DOWNSTRM        r+c           t          p
</pre>

RT=D shows travel rates rule for uniform rate, relating rate time and distance.


{{{system((r-c)t=n,(r+c)t=p)}}}


{{{system(rt-ct=n,rt+ct=p)}}}


{{{system(tr-tc=n,tr+tc=p)}}} , notice that terms are arranged so known coefficient on left
and unknown variable on the right, IN EACH TERM, in the left members.




Elimination Method can be used as a start.
{{{tr-tc+tr+tc=n+p}}}
{{{2tr=n+p}}}
{{{highlight(r=(n+p)/(2t))}}}


{{{tr-tc-tr-tc=n-p}}}
{{{-2tc=n-p}}}
{{{2tc=p-n}}}
{{{highlight(c=(p-n)/(2t))}}}


Substitute the given assigned values to evaluate r and c.