$${\mathtt{x}} = {\mathtt{5}}$$
You can find the answer by substituting x many times. To the fifth time, the answer will equal 52 and 52. I will show you.
$$10x+2=12+8x=10*5+2=12+8*5$$
Now, multiply.
$${\mathtt{10}}{\mathtt{\,\times\,}}{\mathtt{5}} = {\mathtt{50}}$$
$${\mathtt{8}}{\mathtt{\,\times\,}}{\mathtt{5}} = {\mathtt{40}}$$
Now, you add.
$${\mathtt{50}}{\mathtt{\,\small\textbf+\,}}{\mathtt{2}} = {\mathtt{52}}$$
$${\mathtt{40}}{\mathtt{\,\small\textbf+\,}}{\mathtt{12}} = {\mathtt{52}}$$
Now, let's compare them.
$${\mathtt{52}} = {\mathtt{52}}$$
So, the equation is true.
Hope it helps!