An office building has three air conditioning units, one for each office. each unit runs only when employees are working. the tables below show the number of hours employees worked at each office over a three-month period and the total air conditioning electric costs for the entire office for each month. number of hours worked unit a unit b unit c june 184 207 276 july 174 198 264 august 168 189 242 total air conditioning electric costs june $142.60 july $135.96 august $128.30 how much does it cost to run unit a per hour?