A belt drive system consists of the wheels A, B and C, which rotate smoothly. Wheel
B turns 4 full rounds when wheel A turns 5 full rounds. Wheel B turns 6 full rounds when
wheel C turns 7 full rounds. Find the perimeter of wheel A if the perimeter of wheel C is 30cm.
(A) 27 cm
(B) 28 cm
(C) 29 cm
(D) 30 cm
(E) 31 cm