Third one
15,000,000 ohms because M=10^6
Answer:

Explanation:
Cold water in: 
Hot water in: 

Step 1: Determine the rate of heat transfer in the heat exchanger




Step 2: Determine outlet temperature of hot water



Step 3: Determine the Logarithmic Mean Temperature Difference (LMTD)










Step 4: Determine required surface area of heat exchanger



Step 5: Determine length of heat exchanger


