Giải:
\(\begin{array}{l}a)\,121 - \left( {118 - x} \right) = 217\\ \Leftrightarrow \,121 - 118 + x\,\,\,\,\, = 217\\ \Leftrightarrow \,\,\,\,\,\,\,\,\,3\,\,\,\,\,\,\,\,\,\, + x\,\,\,\,\,\, = 217\\ \Leftrightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\, = 217 - 3\\ \Leftrightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\, = 214\\b)\,\left[ {\left( {6x - 39} \right):7} \right].4 = 12\\ \Leftrightarrow \,\,\left( {6x - 39} \right):7 = 3\\ \Leftrightarrow \,\,\,\,\,\,6x - 39\,\,\,\,\,\,\, = 21\\ \Leftrightarrow \,\,\,\,\,\,6x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 60\\ \Leftrightarrow \,\,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 10\\c)\,11x - 7x + x = 325\\ \Leftrightarrow \,\,\,\,\,\,5x = 325\\ \Leftrightarrow \,\,\,\,\,\,\,\,x = 325:5\\ \Leftrightarrow \,\,\,\,\,\,\,\,x\, = 65\\d)\,15 - x = 7 - \left( { - 2} \right)\\ \Leftrightarrow \,15 - x\, = 9\\ \Leftrightarrow \,\,\,\,\,\,\,\,\,\,\,x = \,15 - 9\\ \Leftrightarrow \,\,\,\,\,\,\,\,\,\,\,x = 6\\e)\,x - \left[ {42 + \left( { - 28} \right)} \right] = - 8\\ \Leftrightarrow x - \,\,14\,\,\,\,\,\, = - 8\\ \Leftrightarrow x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 14 - 8\\ \Leftrightarrow x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 6\end{array}\)
