11. A belt drive system consists of the wheels $K, L$ and $M$, which rotate without any slippage. The wheel $L$ makes 4 full turns when $K$ makes 5 full turns; also $L$ makes 6 full turns when $M$ makes 7 full turns.
The perimeter of wheel $M$ is $30 \mathrm{~cm}$. What is the perimeter of wheel $K$ ?

A $27 \mathrm{~cm}$
B $28 \mathrm{~cm}$
C $29 \mathrm{~cm}$
D $30 \mathrm{~cm}$
E $31 \mathrm{~cm}$
11. B To compare wheels $K$ and $M$, we need to find the lowest common multiple of 4 and 6 , which is 12 . When wheel $L$ makes 12 turns, wheel $K$ makes 15 turns and wheel $M$ makes 14 turns. When wheel $L$ makes 24 turns, wheel $K$ makes 30 turns and wheel $M$ makes 28 turns, so the ratio of the circumferences of wheel $K$ to wheel $M$ is 28:30.