The cost per unit of electricity during a 4 year period is as follows: Year 1, $3 per unit; Year 2, $4 per unit; Year 3, $5 per unit; Year 4, $6 per unit. If a factory spent equal dollars on electricity each year, what was the average cost of a unit of electricity during the 4 year period?
Choose the correct answer:
A) $4.31
B) $4.51
C) $4.21
D) $5.21
E) $5.61
Let money spent each year = $60   Units bought first year = 20   Units bought second year = 15   Units bought third year = 12   Units bought fourth year = 10   Total number of units = 57   Total money spent = 60*4= 
<gadget id="calculator">60*4</gadget>
<output>240</output>
240   Average= 240/57 = 4.21   Answer : $4.21
<result>C</result>
The cost per unit of electricity during a 4 year period is as follows: Year 1, $3 per unit; Year 2, $4 per unit; Year 3, $5 per unit; Year 4, $6 per unit. If a factory spent equal dollars on electricity each year, what was the average cost of a unit of electricity during the 4 year period?