Question

Can someone tell me if this is right thanks

Answer 1

bearing in mind that an absolute value expression is in effect a piece-wise expression, because it has a ± version.

$\bf 3|x|+7=28\implies 3|x|=21\implies |x|=\cfrac{21}{3}\implies |x|=7\implies \begin{cases} +(x)=7\\ -(x)=7 \end{cases} \\\\[-0.35em] ~\dotfill\\\\ +(x)=7\implies \boxed{x=7}~\hfill -x=7\implies \boxed{x=-7}$

Answer 2

Yeah because 31x1+7-7=28-7=21