In an experiment investigating the rate of photosynthesis in Cabomba pondweed, a light source is placed at a distance of 20 cm from the plant. Under these conditions, where light intensity is the limiting factor, the rate of photosynthesis is measured to be 80 bubbles per minute80\text{ bubbles per minute}80 bubbles per minute.
The light source is then moved to a distance of 50 cm from the pondweed.
Assuming the rate of photosynthesis is directly proportional to the light intensity, which of the following is the expected rate of photosynthesis at this new distance, to the nearest whole bubble per minute?
32 bubbles per minute32\text{ bubbles per minute}32 bubbles per minute
50 bubbles per minute50\text{ bubbles per minute}50 bubbles per minute
13 bubbles per minute13\text{ bubbles per minute}13 bubbles per minute
200 bubbles per minute200\text{ bubbles per minute}200 bubbles per minute