1st.expand the first 2 brackets
(x+3)(x+3)(x+3)
(x(x+3)+3(x+3))(x+3)
[tex]( {x}^{2} + 3x + 3x + 9)(x + 3)[/tex]
2nd.expand the last 2 brackets remaining
[tex]x( {x}^{2} + 6x + 9) + 3( {x}^{2} + 6x + 9)[/tex]
[tex] {x}^{3} + 6 {x}^{2} + 9x + 3 {x}^{2} + 18x + 27[/tex]
[tex] {x}^{3} + 9 {x}^{2} + 27x + 27[/tex]
