The resistance is directly proportional to the length of the wire. This means that if the length increased so does the resistance. They are linked by the equation R is directly proportional to length over area R=l/a. so this means that the 30cm wire will have thrice the resistance of the 10cm wire if the area of cross-section of both thee wires is the same.

The daily cost becomes 2kw * 2 which equals = 4kwhr.

Now we calculate the cost of running it for 30 days which becomes 4 * 30= 120Kwh

Now we multiply it by the cost of a unit thereby we get : 4*120= 480 rupees.