Question 955501
{{{0.200mL=0.2L}}}
{{{1.2L}}}= 1,2 l
The ratio of concentrate to water is
{{{0.2/1.2=highlight(1/6="1 : 6")}}} ,
meaning {{{1}}} part of concentrate to {{{6}}} parts of water.
 
In this problem (and in many that look like this one),
volumes are additive, so mixing {{{0.2L}}} concentrate and {{{1.2L}}} water
yields {{{0.2L+1.2L=1.4L}}} of the mixture.
So, to make {{{1.4L}}} of the mixture you need {{{0.2L}}} concentrate,
a concentrate to mix ratio of {{{0.2/1.4=1/7="1 : 7"}}} ,
and you need {{{1.2L}}} water,
for a water to mix ratio of {{{1.2/1.4=6/7="6 : 7"}}} .
So, to make {{{14L}}} of the drink mixture you need
{{{(14L)*(6/7)=12L}}} of water.
That was obvious, 
because you could make {{{1.4L}}} drink mixture
by mixing {{{0.2L}}} concentrate and {{{1.2L}}} water,
so to make {{{1.4L}}} , which is {{{14L/"1.4 L"=10}}} times as much
you would need to mix
{{{10*(0.2L)=2L}}} concentrate and
{{{10*(1.2L)=12L}}} of water.
  
NOTES:
I prefer using {{{L}}} for liter; I think it is customary for chemists like me, Maybe it is required for chemists, but I do not remember exactly why I do it.
Also, I currently live in the USA, so I use a decimal dot instead of a decimal comma,
and when I say a billion I mean a 1 followed by 9 zeros, which I write in groups of 3 zeros, separates by commas, as in {{{"1,000,000,000"}}} .
Other countries use a decimal dot, and when they mean 1 billion, they write a 1 followed by 12 zeros, which they write in groups of 3 zeros, separates by dots, as in {{{"1.000.000.000.000"}}} .
Sadly, math is not yet universal.
 
In real life, volumes mixed are not exactly additive (as a chemical engineering professor would tell you),
but it is usually close enough for everyday purposes,
and I bet your math teacher is not a chemical engineer anyway,
and does not know that volumes could change on mixing.