Question 106053
If {{{12}}} is subtracted from three times a number, we can write it as
{{{3x-12}}}

and the difference is multiplied by {{{2}}}, we can write it as

{{{(3x-12)2}}}


and if the result is {{{-42}}},we can write it as

{{{(3x-12)2 = -42}}}

  Find the number:

{{{(3x-12)2 = -42}}}   ---- both sides divide by {{{2}}}
{{{3x - 12 = -21}}}    ---- add {{{+12}}} to both sides

{{{3x - 12 + 12 = -21 + 12}}}


{{{3x = -9}}}---- both sides divide by {{{3}}}

{{{x = -3}}}

check:

{{{(3x-12)2 = -42}}}   

{{{(3*(-3) -12)2 = - 42}}}

{{{(-9 -12)2 = 42}}}
{{{-21*2 = -42}}}
{{{-42 = -42}}}