The heat of combustion of $CH_4$, $C$(graphite) and $H_{2(g)}$ are respectively $20\;kcal$, $40\; kcal$ and $-10\; kcal$. The heat of formation of $CH_4$ is :

Question

( A ) $+40$ kcal
( B ) $80$ kcal
( C ) none of these
( D ) $40$ kcal