$\Rightarrow 10[\sin A+\sin B]$

where

$B=2 \pi(100 t-0.02 x)$ and

$A=2 \pi(100 t+0.02 x)$

Thus,

$\Rightarrow 10\left[2 \sin \frac{A+B}{2} \sin \frac{A-B}{2}\right]$

$\Rightarrow 20 \sin (2 \pi 100 t) \sin (2 \pi 0.02 x)$

Comparing the above equation with standard standing wave equation, we get amplitude $=20$ and wave vector

$k=\frac{2 \pi}{\lambda}=2 \pi \times 0.02 \Rightarrow \lambda=50$

Therefore, the loop length $=\frac{\lambda}{2}=25$