If the straight line $x=b$ divide the area enclosed by $y=(1-x)^{2}, y=0$ and $x=0$ into two parts $R_{1}(0 \leq x \leq b)$ and $R_{2}(b \leq x \leq 1)$ such that $R_{1}-R_{2}=\frac{1}{4}$, Then, $b$ equals to $\quad$ [Single Correct Optlon 2011]
(a) $\frac{3}{4}$
(b) $\frac{1}{2}$
(c) $\frac{1}{3}$
(d) $\frac{1}{4}$