\(\begin{array}{l}
a)\,\,4\left( {x - 3} \right) + 6 = 120:{2^2}\\
4\left( {x - 3} \right) + 6 = 120:4\\
4\left( {x - 3} \right) + 6 = 30\\
4\left( {x - 3} \right) = 30 - 6\\
4\left( {x - 3} \right) = 24\\
x - 3 = 24:4\\
x - 3 = 6\\
x = 6 + 3\\
x = 9\\
b)\,\,182 - 2x:14 = 178\\
2x:14 = 182 - 178\\
2x:14 = 4\\
2x = 4.14\\
2x = 56\\
x = 56:2\\
x = 28\\
c)\,\,66\,\, \vdots \,\,x\,\,;\,\,84\,\, \vdots \,\,x\,\,;\,\,90\,\,\, \vdots \,\,x\,\,va\,\,3 < x < 10\\
\Rightarrow x \in UC\left( {66;84;90} \right)\\
Ta\,\,co:\,\,66 = 2.3.11;\,\,\,\,\,\,84 = {2^2}.3.7\,\,;\,\,\,\,\,90 = {2.3^2}.5\\
\Rightarrow UCLN\left( {66;84;90} \right) = 2.3 = 6\\
\Rightarrow UC\left( {66;84;90} \right) = \left\{ {1;2;3;6} \right\}\\
Ma\,3 < x < 10\,\, \Rightarrow x = 6.
\end{array}\)
