The cost per unit of electricity during a 4 year period is as follows:
Year 1, $2 per unit;
Year 2, $3 per unit;
Year 3, $4 per unit;
Year 4, $5 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 choice from the following options.
A) $3.82  B) $3.62  C) $5.12  D) $3.12  E) $4.12
Let money spent each year = $60   Units bought first year = 30   Units bought second year = 20   Units bought third year = 15   Units bought fourth year = 12   Total number of units = 77   Total money spent = 60*4= 
<gadget id="calculator">60*4</gadget>
<output>240</output>
240   Average= 240/77 = 3.12   Answer : $3.12
<result>D</result>
The cost per unit of electricity during a 4 year period is as follows:
Year 1, $2 per unit;
Year 2, $3 per unit;
Year 3, $4 per unit;
Year 4, $5 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?