Coal and crude oil are made from the remains of plants and animals that died long ago. The primary energy source in an ecosystem is the sun. Plants take in energy from the sun to produce high energy molecules which are transferred along the food chain to animals. When these plants and animals die, the high energy molecules are now stored in fossil fuels. Recall that the molecules were formed using energy from the sun, therefore, the sun is the energy source from which the high energy molecules contained in fossil fuels are obtained.
To find the answer you can set up an equation like this: 3(x)(d) x would stand for number of cans each dog eats, while d stands for the number of days in a week. 3(2)(7)=42 Sam would have to purchase 42 cans of dog food each week.
