The figure above represents BOTH plates, one on top of the other.
5-holed plate:
The ring of PINK circles represents the 5-holed plate.
Since 360/5 = 72, the pink circles are spaced 72° apart.
A=0°, B=72°, D=144°, F=216°, H=288°.
4-holed plate:
The ring of BLUE circles represents the 4-holed plate.
Since 360/4 = 90, the blue circles are spaced 90° apart:
A=0°, C=90°, E=180°, G=270°.
The least distance between any two circles -- 18° -- occurs between B and C and between G and H.
If the pink ring rotates 18° clockwise, B will move on top of C and G will move on top of H.
If the blue ring rotates 18° counter-clockwise, C will move on top of B and H will move on top of G.
Thus, for one hole to land on top of another, the least number of degrees that one of the plates must rotate is 18°.
The correct answer is
C.
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