Answer:
[tex]a. \: 3( {x}^{2}) ^{6} (2 {x}^{3} )^{4} \\ 3( {x}^{12} )(16 {x}^{12} ) \\ (3 {x}^{12} )(16 {x}^{12} ) \\ = 48 {x}^{24} [/tex]
[tex]b. \: 5 {x}^{5} \times - 3 {x}^{2} \\ = - 15 {x}^{7} [/tex]
I hope I helped you^_^
