solving without using any Algorithim.
$M\left ( 100 \right )$=$M\left ( M\left ( 99 + 11 \right ) \right )$
=$M\left ( 101 \right )$
$\because M\left ( 111 \right )=111-10=101$
=$91$
Now, $M \left ( 99 \right )$ = $M \left ( \left M ( 99+11 \right ) \right )$
=$M\left ( M\left ( 110 \right )\right ) $
=$M\left ( 100 \right )=91$