The petrol consumption of a car (y miles per gallon) depends on the speed the car is travelling at (x mph), according to the formula y= 200-1.5x - 4500/x

a.) draw the graph of this equation for 40 <= x <= 80, taking a scale of 2 cm to 5 units on each axis.
b.) what is the petrol consumption at 75 mph
c.) use your graph to estimate the most economical speed at which to drive this car. ​

Farmers know that driving heavy equipment on wet soil compresses the soil and injures future crops. here are data on the "penetrability" of the same type of soil at two levels of compression. penetrability is a measure of how much resistance plant roots will meet when they try to grow through the soil. compressed soil 2.85 2.66 3 2.82 2.76 2.81 2.78 3.08 2.94 2.86 3.08 2.82 2.78 2.98 3.00 2.78 2.96 2.90 3.18 3.16 intermediate soil 3.17 3.37 3.1 3.40 3.38 3.14 3.18 3.26 2.96 3.02 3.54 3.36 3.18 3.12 3.86 2.92 3.46 3.44 3.62 4.26 use the data, omitting the high outlier, to give a 95% confidence interval for the decrease in penetrability of compressed soil relative to intermediate soil. compute degrees of freedom using the conservative method. interval: to