Final answer:
Roughly 6 to 7 sixty-watt light bulbs would use the same power as a 68-kg cyclist riding at 15 km/h, assuming the cyclist is using 400 watts of metabolic energy at a moderate cycling speed.
Step-by-step explanation:
Assuming that the cyclist uses metabolic energy similar to the reference case of 400 W when cycling at a moderate speed, we can calculate how many light bulbs would use the same power. A single 60-watt light bulb uses 60 watts of power. To find out how many 60-watt light bulbs would use the same power as a cyclist, we divide the cyclist's power usage by the power usage of a light bulb.
400 watts (cyclist's power) ÷ 60 watts (per light bulb) = 6⅓6; (or approximately 6.67 light bulbs)
Thus, about 6 to 7 sixty-watt light bulbs would use the same power as a 68-kg cyclist riding at 15 km/h.