$4.$ Calculate the amount of water that must be supplied to a heat exchanger that cools $100$kg$/$ h of tomato paste from $90$C to $20$C$.$ The tomato paste contains $40\%$ solids. The increase in water temperature should not exceed $10$C while passing through the heat exchanger. There is no mixing of water and tomato paste in the heat exchanger. The reference temperature is $10$C$.$