Answer:
m is 7
Step-by-step explanation:
[tex]{ \sf{ - 6(1 + 8m) = - 342}}[/tex]
divide all sides by (-6) :
[tex]{ \sf{ \frac{ - 6(1 + 8m)}{ - 6} = \frac{ - 342}{ - 6} }} \\ \\ { \sf{1 + 8m = 57}}[/tex]
make m the subject:
[tex]{ \sf{8m = 56}} \\ { \sf{m = 7}}[/tex]