Find the area of a semi-circle whose radius is 7cm. [Take π = 22/7]

$$
4P = 4 \begin{pmatrix} 4 \\ 3 \end{pmatrix} = \begin{pmatrix} 4 \times 4 \\ 4 \times 3 \end{pmatrix} = \begin{pmatrix} 16 \\ 12 \end{pmatrix}
$$

$$
2Q = 2 \begin{pmatrix} 2 \\ -1 \end{pmatrix} = \begin{pmatrix} 2 \times 2 \\ 2 \times -1 \end{pmatrix} = \begin{pmatrix} 4 \\ -2 \end{pmatrix}
$$

$$
4P - 2Q = \begin{pmatrix} 16 \\ 12 \end{pmatrix} - \begin{pmatrix} 4 \\ -2 \end{pmatrix}
$$
$$
4P - 2Q = \begin{pmatrix} 16 - 4 \\ 12 - (-2) \end{pmatrix}
$$
$$
4P - 2Q = \begin{pmatrix} 12 \\ 12 + 2 \end{pmatrix}
$$
$$
4P - 2Q = \begin{pmatrix} 12 \\ 14 \end{pmatrix}
$$
The calculated result is $\begin{pmatrix} 12 \\ 14 \end{pmatrix}$. This answer is not among the given options.

$$
\begin{pmatrix} -5 \\ 12 \end{pmatrix} = \begin{pmatrix} 10x \\ 12 \end{pmatrix}
$$

$$
-5 = 10x
$$

$$
x = \frac{-5}{10}
$$
$$
x = -\frac{1}{2}
$$
The value of x is $\boxed{\text{B. } -\frac{1}{2}}$.