In this question, x represents the quantity demanded in units of 1000, and p represents unit price in dollars.
The equation of the demand curve is 3x + 4p - 48 = 0. We rewrite this equation in the slope-intercept form as follows: 4p = -3x + 48. This is further simplified to p = -0.75x + 12. The demand curve is linear. From the slope-intercept form of the equation, we can see that the slope of the line is -0.75; the line intercepts the y-axis (price) at 12.
To plot the demand curve, use the equation p = -0.75x + 12 to find the coordinates of two points on the line: for example, (0, 12) and (16,0). Join these two points using a straight line, as shown in the diagram below.