Question 167032
Let x=amount of the $30 coffee needed

($ understood)
Now we know that the value of the $30 coffee (30x) plus the value of the $60 coffee (60*90) has to equal the value of the final mixture(40* (90+x)).  So our equation to solve is:

30x+60*90=40(90+x)  get rid of parens and simplify
30x+5400=3600+40x subtract 30x and also 3600 from each side
30x-30x+5400-3600=3600-3600+40x-30x  collect like terms
1800=10x  divide each side by 10
x=180 lbs -------------amount of $30 coffee needed

CK
30*180+60*90=40*270
5400+5400=10800
10800=10800

Hope this helps---ptaylor