I couldn't come up with anything but D... Water costs zero so shouldn't it be accounted for..?

I think the reason E is correct over D, is because revenue in this case is based off of total liters. So the final equation must contain the total number of liters of water.

water - w
syrup - m

for every liter of syrup each liter of water is required

total mixture = wm+m

selling price = j per liter
Therefore = j(wm+m)

cost price = k per liter
since water costs nothing total cost will be km

gross profit = selling price - cost price

=> j(wm+m) - km
=> jm(w+1) - km

Hence E is the answer.

Awesome explanation

parallel_chase wrote:water - w
syrup - m

for every liter of syrup each liter of water is required

total mixture = wm+m

selling price = j per liter
Therefore = j(wm+m)

cost price = k per liter
since water costs nothing total cost will be km

gross profit = selling price - cost price

=> j(wm+m) - km
=> jm(w+1) - km

Hence E is the answer.