differentiate 3x4(x+2)
$$3*4(x+2) \\=12(x+2) \\=12x+24 \\ \\\frac{\ d (12x+24)} { dx } = \frac{\ d (12x)} { dx }+\frac{\ d (24)} { dx } \\ \\\frac{\ d (12x+24)} { dx } = 12+0 \\ \\\frac{\ d (12x+24)} { dx } = 12$$
$$\\ \frac{d}{dx}\;3\times 4(x+2)\\\\ =12\times\frac{d}{dx}(x+2)\\\\ =12\times 1\\\\ =12$$
