A uniform rod $A B$ of mass $2 \mathrm{~kg}$ and length $1 \mathrm{~m}$ is placed on a wedge $\mathrm{O}$. To keep the rod horizontal, its end $\mathrm{A}$ is tied with a thread and the spring has tension $6 \mathrm{~N}$. The reaction of support $\mathrm{O}$ on the rod when the thread is burnt is
(a) $15 \mathrm{~N}$
(b) $40 \mathrm{~N}$
(c) $20 \mathrm{~N}$
(d) $25 \mathrm{~N}$