50(lb) X 16 = 800 oz of powder
Cost $0.10 per oz of powder ($80 / 800)
$2.00 worth of powder (20 x $0.10) makes 7 pints
$2 / 7 = $0.285 cost per pint
There are 8 pints in a gallon
Every gallon costs $2.28
You should be able to figure out everything else you need from the above information.