4.70= acid in 40% solution
4.70/70+w = .28
30 liters of water is needed
you have to subtract the amount of money chuck earned ($72.50) by the cost of the gas for the mower ($11.25) and the new string for the trimmer he bought ($7.75).
and then subtract $61.25 by the second thing he bought (the new string for the trimmer)
so in total it's $53.50 (53 dollars and 50 cents)