The expression would be $0.20 x f. Once you figure out what the 'f' variable stands for, you have to multiply it by $0.20, and you will have your answer.
Pigments are colored chemical compounds that absorb light and produce color.
Chlorophyll is an example of a pigment. It is a green pigment found in chloroplasts of plants, algae, and bacteria. It is vital to the performance of photosynthesis in plants.
For photosynthesis to occur, four factors must be present. Sunlight, carbon dioxide, water, and chlorophyll.