Question 124265
It is given that there will be 70 lb of mixture of the teas
Also given is that the mixture will sell for $2.75 / lb.
Let {{{a}}} = lbs of $3.45 tea
Let {{{b}}} = lbs of $1.75 tea
Since {{{a}}} and {{{b}}} account for the whole mixture,
{{{a + b = 70}}}
multiply both sides by -1.75
(1){{{-a*1.75 - b*1.75 = -122.5}}} 
{{{(a*3.45) + (b*1.75) = 70*2.75}}}
(2){{{(a*3.45) + (b*1.75) = 192.5}}}
Add (1) and (2)
{{{a*1.7 = 70}}}
{{{a = 41.176}}}
{{{b = 70 - 41.176}}}
{{{b = 28.823}}}
check
(1){{{-a*1.75 - b*1.75 = -122.5}}} 
{{{(a*3.45) + (b*1.75) = 70*2.75}}}
{{{41.176*3.45 + 28.823*1.75 = 70*2.75}}}
{{{142.057 + 50.44 = 192.5}}}
{{{192.497 = 192.5}}} close enough
So, I get {{{41.176}}} lbs of the $3.45 tea and
{{{28.823}}}lbs of the $1.75 tea