M of x,y is just a number and you multiply that times a vector so M of x,y right over here is going to be a scalar function when you multiply by i it becomes a vector that's going to give you a speed and then N of x,y is also going to give you a speed and it tells you a speed in a j direction so it becomes a vector and a speed in the i direction becomes a vector as well but these speeds, the units of speed (let me write this over here) so now we're talking about in particular M of x,y and N of x,y that would be in units of distance per time and so maybe for this example we'll say the units are meters per second