For a private investigator who requires a 750 retainer fee plus 115 per hour, let x represent the number of hours the investigator spends working on a case. What is the equation representing the total cost?
a) Total cost = 750 + 115x
b) Total cost = 750 - 115x
c) Total cost = 115 + 750x
d) Total cost = 750x² + 115
