Question 984530
{{{-12 + 3b -1 = -5 -b}}}.....add {{{b}}} to the both sides

{{{-12 + 3b+b - 1 = -5- b+b}}}

{{{-12 + 3b+b – 1 = -5 - cross(b)+cross(b)}}}

{{{-12 + 4b - 1 = -5}}}.....add {{{12}}} to the both sides

{{{-12 +12+ 4b - 1 = -5+12}}}

{{{-cross(12) + cross(12)+ 4b -1 = -5+12}}}

{{{ 4b - 1 = 7}}}.....add {{{1}}} to the both sides

{{{ 4b – 1+1 = 7+1}}}

{{{ 4b – cross(1)+cross(1) = 8}}}

{{{ 4b  = 8}}}......both sides divide by {{{4}}}

{{{ 4b/4  = 8/4}}}

{{{ b  = 2}}}