Ans: C
$\begin{array}{rcl}
a(a + b) & = & 2(b – a) \\
a^2 + ab & = & 2b – 2a \\
ab – 2b & = & -a^2 – 2a \\
b(a – 2) & = & -(a^2 + 2a) \\
b & = & \dfrac{-(a^2 + 2a)}{a – 2} \\
b & = & \dfrac{a^2 + 2a}{2 – a}
\end{array}$
$\begin{array}{rcl}
a(a + b) & = & 2(b – a) \\
a^2 + ab & = & 2b – 2a \\
ab – 2b & = & -a^2 – 2a \\
b(a – 2) & = & -(a^2 + 2a) \\
b & = & \dfrac{-(a^2 + 2a)}{a – 2} \\
b & = & \dfrac{a^2 + 2a}{2 – a}
\end{array}$
