1. \nWe are given three points: $(-3, a)$, $(0, 4)$, and $(6, 2a)$. We need to find $2a + 4$ given that these points are collinear.\n\n2. \nIf three points are collinear, the slope between any two pairs of points must be the same. Calculate the slope between $(-3, a)$ and $(0, 4)$:\n$$m_1 = \frac{4 - a}{0 - (-3)} = \frac{4 - a}{3}$$\n\n3. \nCalculate the slope between $(0, 4)$ and $(6, 2a)$:\n$$m_2 = \frac{2a - 4}{6 - 0} = \frac{2a - 4}{6}$$\n\n4. \nSet the slopes equal due to collinearity:\n$$\frac{4 - a}{3} = \frac{2a - 4}{6}$$\nMultiply both sides by 6 to clear denominators:\n$$6 \times \frac{4 - a}{3} = 6 \times \frac{2a - 4}{6}$$\n$$2(4 - a) = 2a - 4$$\n\n5. \nSimplify and solve for $a$:\n$$8 - 2a = 2a - 4$$\nAdd $2a$ to both sides:\n$$8 = 4a - 4$$\nAdd 4 to both sides:\n$$12 = 4a$$\nDivide both sides by 4:\n$$a = 3$$\n\n6. \nNow, compute $2a + 4$:\n$$2(3) + 4 = 6 + 4 = 10$$\n\nFinal answer: $10$ (choice \u24b9)