After sewage is processed through sewage treatment plants, what remains is a dried product called sludge. Sludge

Question:

After sewage is processed through sewage treatment plants, what remains is a dried product called sludge. Sludge contains many minerals that are beneficial to the growth of many farm crops, such as corn, wheat, and barley. Thus, large corporate farms purchase sludge from big cities to use as fertilizer for their crops. However, sludge often contains varying concentrations of heavy metals, which can concentrate in the crops and pose health problems to the people and animals consuming the crops. Therefore, it is important to study the amount of heavy metals absorbed by plants fertilized with sludge. A crop scientist designs the following experiment to study the amount of mercury that may be accumulated in the crops if mercury was contained in sludge. The experiment studied corn, wheat, and barley plants with one of six concentrations of mercury added to the planting soil. There were 90 growth containers used in the experiment with each container having the same soil type. The 18 treatments (three crop types and six mercury concentrations) were randomly assigned to five containers each. At a specified growth stage, the mercury concentration in parts per million (ppm) was determined for the plants in each container. The 90 data values are given here. Note that there are 5 data values for each combination of type of crop and mercury concentration in the soil.

a. Graph the above data with separate symbols for each crop.
b. Does the relationship between soil mercury content and plant mercury content appear to be linear? Quadratic?
c. Does the relationship between soil mercury content and plant mercury content appear to be the same for all three crops?