100 POINTS + BRAINLIEST! Please explain as well.

A railroad's track can be determined using the following graph.

Linear function decreasing from the left in quadrant 2 passing through the point 0 comma 5 and 8 comma 0.

Several different roadways are in the same region as the railroad.

Part A: A highway's path can be found using the equation 2x + 3y = 21. Use the graphs of the functions to determine the number of intersections there will be between the railroad and the highway, and explain completely. (5 points)

Part B: A turnpike's route is determined by the equation y equals one third times x squared period Prove algebraically how many intersections there will be between the railroad and the turnpike, showing all necessary work. (5 points)