Sorasyn, these are great examples :)
With you first example
$$\left({\frac{{\mathtt{4}}}{{\mathtt{5}}}}\right){\mathtt{\,\small\textbf+\,}}\left({\frac{{\mathtt{4}}{\mathtt{\,\times\,}}{\mathtt{x}}}{{\mathtt{7}}}}\right) = {\mathtt{6}}$$
It is easier if you multiply both sides by 35 right from the beginning.
$${\mathtt{35}}{\mathtt{\,\times\,}}\left(\left({\frac{{\mathtt{4}}}{{\mathtt{5}}}}\right){\mathtt{\,\small\textbf+\,}}\left({\frac{{\mathtt{4}}{\mathtt{\,\times\,}}{\mathtt{x}}}{{\mathtt{7}}}}\right)\right) = {\mathtt{35}}{\mathtt{\,\times\,}}{\mathtt{6}}$$
$$\left({\mathtt{7}}{\mathtt{\,\times\,}}{\mathtt{4}}\right){\mathtt{\,\small\textbf+\,}}\left({\mathtt{5}}{\mathtt{\,\times\,}}{\mathtt{4}}{\mathtt{\,\times\,}}{\mathtt{x}}\right) = {\mathtt{210}}$$
$${\mathtt{28}}{\mathtt{\,\small\textbf+\,}}{\mathtt{20}}{\mathtt{\,\times\,}}{\mathtt{x}} = {\mathtt{210}}$$
.