What is equivelent to
4d+6+2d

4d+6+2d can be reduced to 6d+6

This can also be rewritten as 6(d+1).

We can add like terms. Like terms are when the variables are alike, so you can add them to get a simpler form of your expression.equation.
4d and 2d are like terms, therefore, we can add them.

6d+6 is what we are left with.

Our final 6d+6 is equivalent to 4d+6+2d

Figure it out your self