A.
100%=all
so if 25% is dark and the rest is milk then
dark+milk=all
25%+milk=100%
minus 25% both sides
milk=75%
so
if milk chocolate=3lb then
3lb=75%
divide by 3
1lb=25%=dark chocolate
oops, I didn't use an equation
hmm
ratios and things
75%=milk
25%=dark
so we got
for m=pounds of milk chocolate
and d=dark chocolate
m/d=72/25 or m/d=3 and
m=3
duh
3/d=3
3=3d
1=d
B. 1 lb dark chocolate