Let C denote the 60% solution and D denote the final 76% solution.
We have 6 lbs of 100% solution.
Using the method of alligation.
24= 76 - 100
16= 60 - 76
E.g. There are 16 parts of C for every 24 parts of D
then there are 6 parts of z, since (16/24)=6/z
x= 9.0= 6/(16/24) lbs of 60% solution to add to your 6 lbs of 100% solution.
y= 15.0= (6+9.0) lbs of the final 76% solution.
check
0.6 * 9.0 + 1 * 6 = 0.76*(6+9.0)
5.4 + 6 = 0.76*(15.0)
11.4 = 11.4
ok
100 16 6 lbs of 100% solution
76 15 lbs of 76% solution
60 24 24/16*6=9 lbs of 60% solution
40
15 lbs of 76% solution