3(x+y)
distribute 3 to both variables in parentheses.
3x+3y
they can not be added because they have different variables.
7d+3(d+8)-6
distribute 3 first because it is outside of the parentheses.
7d+3d+24-6
then add the numbers that share the same variable.
10d + 18
they can not be added because of different variables.
