A binomial squared is solved with this formula:
[tex](a+b)^2=a^{2}+2ab+b^{2}[/tex]In this exercise, a = 3h and b=3:
[tex](3h+3)^2=(3h)^2+2\cdot3h\cdot3+3^{2}[/tex]We solve the square in the first and third term and multiply all the numbers in the second term
[tex](3h+3)^2=3^2\cdot h^{2}+18h+81[/tex]And finally we have
[tex](3h+3)^{2}=9h^{2}+18h+81[/tex]