Đáp án:
$\begin{array}{l}
a)8x + 2x = 25.2\\
\Leftrightarrow 10x = 50\\
\Leftrightarrow x = 50:10 = 5\\
Vậy\,x = 5\\
b)5x + x = 9.16\\
\Leftrightarrow 6x = 144\\
\Leftrightarrow x = 24\\
Vậy\,x = 24\\
c)7x - 2x = 121 + 16.14\\
\Leftrightarrow 5x = 121 + 224\\
\Leftrightarrow 5x = 345\\
\Leftrightarrow x = 69\\
Vậy\,x = 69\\
d)5x + x = 150:2 + 3\\
\Leftrightarrow 6x = 75 + 3\\
\Leftrightarrow 6x = 78\\
\Leftrightarrow x = 13\\
Vậy\,x = 13\\
e)5x + 3x = 729:27.4 + 12\\
\Leftrightarrow 8x = 108 + 12\\
\Leftrightarrow 8x = 120\\
\Leftrightarrow x = 15\\
Vậy\,x = 15\\
f)15x - 2x = 39.12\\
\Leftrightarrow 13x = 39.12\\
\Leftrightarrow x = 39.12:13\\
\Leftrightarrow x = 3.12\\
\Leftrightarrow x = 36\\
Vậy\,x = 36
\end{array}$
