Q$-7$: Under the influence of a triangular distributed load acting on the right edge of the block of weight $W=qb$ in the figure, what should be the minimum horizontal width $"a"$ of the block for tipping to occur at end A$?$

A$)a=\frac{b}{6}$

B$)a=\frac{b}{3}$

C$)a=3b$

D$)a=\frac{2b}{3}$