To find the derivative of y with respect to x, we use the chain rule of differentiation, which states that if y = f(g(x)), then dy/dx = f'(g(x)) * g'(x).
In this case, we have y = 3 sin(-4x), so f(g(x)) = 3 sin(g(x)) and g(x) = -4x. Therefore, f'(g(x)) = 3 cos(g(x)) and g'(x) = -4.
Plugging these values into the chain rule, we get:
dy/dx = f'(g(x)) * g'(x) = 3 cos(-4x) * (-4) = -12 cos(4x)
Therefore, the correct answer is: -12x cos(-4x).