Given that y varies directly with x, use the specified values to write a direct variation equation that relates x and y

If y varies directly as x, then y must be a function of x, or y = a * x. Looking at the values of y (12) and x (4), and putting them in the equation y = ax, we get 12 =a*4 , or a = 3. hence y = 3x must be the the equation that relates x and y.