Respuesta :

apologiabiology
so pure=100%
x added

100%=1=pure

amount times purity=result

x=amount added
x times 1
6-x times (0.6) for te 60%
they add up to
6 times 0.8
solve
x+(6-x)0.6=6(0.8)
x=3


answer is 3 gallons replaced with 100% acid