Part A. From the problem, we have two sets of data: (1) $180 for 4 days and (2) $325 for 9 days. In formulating relationships as equations, the independent variable is the parameter that we can't control, like time. The dependent variable is the cost of car rental. Thus, we let x be the days and y be the cost. If the equation is linear, its standard form would be: y=mx +b. We use the the two sets of data given to solve for m and b, and complete the equation.
Data point 1 (4,180)
180 = 4m + b
Rearranging, b = 180 - 4m ---> eq 1
Data point 2 (9, 325)
325 = 9m + b ---> eq 2
Substituting eq 1 to eq 2,
325 = 9m + (180-4m)
325-180 = 9m - 4m
5m = 145
m = 29
b = 180 - 4(29) = 64
Therefore, the equation is y = 29x + 64.
Part B. In functional notation, the equation is written as f(x) = 29x + 64.
Part C. To graph the equation, start by making a plot wherein the x-axis is the days while the y-axis is the cost. Then, assign values for x with an interval of 1 unit. See the table shown in the picture. With every value of x, you get a corresponding y value. Then, you plot the points on the cartesian plane. Finally, you connect the data points together forming a straight line.