Question 255693
{{{3x - 4(2x + 1) = 21}}}

The first step here would be to distribute the 4 through the parentheses:

{{{3x - 4(2x) -4(1) = 21}}}
{{{3x - 8x - 4 = 21}}}

Now we combine like terms:

{{{-5x - 4 = 21}}}

Add 4 to both sides:

{{{-5x = 25}}}

Divide both sides by -5:

{{{x = -5}}}