Question 370033
Let A be the number of 10ml bottle, B the number of 25mL bottles.
1.{{{A+B=33}}}
.
.
{{{10A+25B=600}}}
2.{{{2A+5B=120}}}
Multiply eq. 1 by (-2) and add to eq. 2,
{{{-2A-2B+2A+5B=-66+120}}}
{{{3B=54}}}
{{{highlight(B=18)}}}
Then from eq. 1,
{{{A+18=33}}}
{{{highlight(A=15)}}}
.
.
.
Let B be the boat speed, C the river current.
Rate*Time=Distance.
With the current, 
{{{(B+C)4=120}}}
1.{{{B+C=30}}}
Against the current,
{{{(B-C)5=120}}}
2.{{{B-C=24}}}
Add eq. 1 to eq. 2,
{{{B+C+B-C=30+24}}}
{{{2B=54}}}
{{{highlight(B=27)}}}kph
From eq. 1,
{{{27+C=30}}}
{{{highlight(C=3)}}}kph