Answer :
2(3)^2= 18 that is with a(3) squared or 2(3)=6 and 6squared or 6^2 = 36.
If You mean is :
[tex]2a^{2}~~~~~~[just\ subtituted\ a\ into\ 3][/tex]
[tex]2a^{2}\\=2(3)^{2}\\=2(3 \times 3)\\=2(9)\\=18[/tex]
[tex]2a^{2}~~~~~~[just\ subtituted\ a\ into\ 3][/tex]
[tex]2a^{2}\\=2(3)^{2}\\=2(3 \times 3)\\=2(9)\\=18[/tex]