a) \(\left|x\right|-3=1\Rightarrow\left|x\right|=4\)
\(\rightarrow\left\{\begin{matrix}x=-4\\x=4\end{matrix}\right.\)
b) \(7-\left|x\right|=-1\Rightarrow\left|x\right|=8\)
\(\rightarrow\left\{\begin{matrix}x=8\\x=-8\end{matrix}\right.\)
c) \(15-\left|3\cdot x\right|=0\Rightarrow\left|3\cdot x\right|=15\)
\(\rightarrow\left\{\begin{matrix}3\cdot x=15\\3\cdot x=-15\end{matrix}\right.\rightarrow\left\{\begin{matrix}x=5\\x=-5\end{matrix}\right.\)