we know that
volume of a bar of soap=2*4*0.5----> 4 in³
A bar of soap is sold for $3 individually
so
$3/4-----> 0.75 $/in³
A three-pack of the same soap costs $8
so
$8*(3*4)----> 0.67 $/in³
if you buy the three-pack you save-----> [0.75-0.67]=0.08 $/in³
the answer is
$0.08
