What do we get when we take away 12900 from 13800?

1. 900

The correct option is A 900
To take away means to subtract.
So, to find what we get when we take away 12900 from 13800, we have to subtract 12900 from 13800.

$\begin{array}{cccccc}& \text{TTh}& \text{Th}& \text{H}& \text{T}& \text{O}\\ & & 2& 18& & \\ & 1& \text{/}3& \text{/}8& 0& 0\\ -& 1& 2& 9& 0& 0\\ & & & 9& 0& 0\end{array}$

So, we get 900 when we take away 12900 from 13800.