the answer is 60kg!! please help

5. Sludge from a wastewater treatment process contains 70wt% water and 30wt% solids. The sludge is dried such that the final product contains only 25wt% water. How much water must be evaporated for every 100kg of wet sludge input? Answer: 60kg Ensure your solution contains all the elements we have discussed in the lectures: basis, labelled flowchart, degree-of-freedom analysis, mass balances, etc