Answer
$(x^{2}+4)^{1/3}(11x^{2}+12)$
Work Step by Step
We simplify:
$3(x^{2}+4)^{4/3}+x* 4(x^{2}+4)^{1/3}*2x
=(x^{2}+4)^{1/3}[3(x^{2}+4)^{3/3}+4*2x^{2}]
=(x^{2}+4)^{1/3}[3(x^{2}+4)+8x^{2}]
=(x^{2}+4)^{1/3}[3x^{2}+12+8x^{2}]
=(x^{2}+4)^{1/3}(11x^{2}+12)$