Static Torque Balance

A board of negligible mass supports a mass of 10 kg at a distance of 2 m from the support at point A. How much mass must be placed at point B, which is 5 m from point A, in order for the rod to remain horizontal?

a)   2 kg

b)   4 kg

c)   6 kg

d)  10 kg

e)   20 kg