Question 903845
0.9*x+0.3*16=0.5(16+x)
0.9*x+4.8=8+0.5x
0.9x-0.5x=8-4.8
0.4x=3.2
x=8 gallons of 90% is added to 16 gallons of 30%  to get  24 gallons  at 50%
check
0.9*8+0.3*16=0.5(16+8)
7.2+4.8=0.5(24)
12=12
ok