Distribute, Then Collect

Some expressions need both skills. $3\left(x+4\right)+2x$ has like terms hiding inside parentheses. First expand: 3 times x is 3x and 3 times 4 is 12, giving $3x+12+2x$. Now the like terms are in the open, and $3x+2x$ is $5x$, so the result is $5x+12$.

The order matters. The 3 multiplies the whole bracket, so you cannot add it to the 2x first: $3\left(x+4\right)$ is not three plus anything. Parentheses go first, exactly as in the order of operations, and collecting comes after.

Write one step per line: expand, then collect. If the expansion line is wrong, the board refuses it before you build on it.