Okay. To do front-end addition you add the 2 highest value places. And then fill the rest of the places with zeros.
For example:
$${\mathtt{2\,310}}{\mathtt{\,\small\textbf+\,}}{\mathtt{1\,293}}$$
We take the 2 highest value places, which are 23 and 12
$$\mathbf{23}10+\mathbf{12}93$$
Now we add these two numbers.
$${\mathtt{23}}{\mathtt{\,\small\textbf+\,}}{\mathtt{12}} = {\mathtt{35}}$$
How fill the other place values with zeros:
$$\mathrm{35}\textit{00}$$
There we go.
+676 