A copper wire is wound on a wooden frame, whose shape is that of an equilateral triangle. If the linear dimension of each side of the frame is increased by a factor of 3, keeping the number of turns of the coil per unit length of the frame the same, then the self inductance of the coil:
a. decreases by a factor of 9
b. increases by a factor of 27
c. increases by a factor of 3
d. decreases by a factor of 93