Question 13189
In this problem, you first need to distribute the negative sign across the parentheses, which changes the problem to {{{10x - 2x - 3 = 21}}}.

Now that you have done that, all equations are basically solved the same way:

1.  Combine like terms. In this case, your equation changes to {{{8x - 3 = 21}}}.

2.  Get everything with an x on one side and everything without an x on the other side of the equal sign.  In this equation, you need to move -3 to the right side of the equal sign by adding it to both sides of the equal sign:  {{{8x = 24}}}.

3.  Solve for x.  In this equation, divide both sides by 8, which gives you x=3.