The tubes in a heat exchanger have the following dimensions: inside diameter 25 mm, outside diameter 30 mm, length 5 m. They are made of steel with a thermal conductivity of 50 W/m·K. The values of the inside and outside heat transfer coefficients are 1000 and 2000 W/m²·K respectively. The fouling factors are 0.0001 m²·K/W on the inside and 0.0005 m²·K/W on the outside. Calculate the overall heat transfer coefficients based on the inside area and on the outside area. Using both of these values in turn, calculate the rate of heat transfer when the overall temperature difference is 50°C.