4. [6 marks) During the winter months, humans do not actually feel the temperature of the air diectly. What we feel is the temperature of our skin which is determined not only by the temperature T of the air (in C) but also the speed v (in km/h) at which the air is moving. This effect is called wind chill and is modeled by the function W (T, v) = 13.12+ 0.62157 11.37.16 +0.396570.16 !! (a) What will be the feel of the temperature with wind chill when the air speed is 60 km/h and the air temperature is -5C? (b) Determine Wr(-5, 60). What does your result tell you about the wind chill, assuming the current air speed is 60 km/h and the actual air temperature is -5C. (c) Determine W.(-5, 60). Assuming the current air speed is 60 km/h and the actual air temperature is -5C, comment on the magnitude of a change felt when the wind increases by 1 km/h.