Answer:
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
