In very cold weather a significant mechanism for heat loss by the human body is energy expended in warming the air taken into the lungs with each breath. (a) On a cold winter day when the temperature is -20$^\circ$C, what amount of heat is needed to warm to body temperature (37$^\circ$C) the 0.50 L of air exchanged with each breath? Assume that the specific heat of air is 1020 J / kg $\cdot$ K and that 1.0 L of air has mass $1.3 \times 10{^-}{^3} kg$. (b) How much heat is lost per hour if the respiration rate is 20 breaths per minute?