A state department of public safety added 1/3x2+5x miles of highway to connect cool town and brag illegal. It cost the department 3x2-9x thousand dollars to complete each mile of Inter estate which expression shows the total cost in thousands of dollars of creating this highway?

Total cost = $ (x⁴ + 12x³ - 45x²)

Step-by-step explanation:

It is given that a state department of public safety added (1/3) x² + 5x miles of highway to connect CoolTown and Bragville.

So, length of highway; L = (1/3) x² + 5x miles

Cost of highway; C = $3x² - 9x per mile

Thus, total cost = LC

Total cost = ((1/3) x² + 5x) x (3x² - 9x)

Total cost = x⁴ - 3x³ + 15x³ - 45x²

Total cost = $ x⁴ + 12x³ - 45x²