What is the percentage change in the result when we add 50 to a certain number x, instead of subtracting 50 from the same number x?

Answer: Option E

If we take different values of x then,
Let x = 150, then error%
$$\begin{array}{rl}& =\frac{\frac{200-100}{100}}{100}\\ & =100\%\end{array}$$
Again if x = 100, then error%
$$\begin{array}{rl}& =\frac{\left(150-50\right)\times 100}{100}\\ & =200\%\end{array}$$
If we take different value of x,
we get different answer so we can't determine it.