Hmm, that method doesn't seem to work here.

Ok, here's a simpler way of doing it:

Notice that if the lines connect at a right angle, their slopes will be perpendicular. So, solve for the slope of the line connecting the refinery and the harbor. Once you have the slope, recall that if a slope is perpendicular that means it's slope is the negative reciprocal.

So, take the negative reciprocal of the slope that you find. Then, use the point on the line that you already have (210,57) to find the equation for that line in the form:

Then, find the equation of the line joining the refinery and the harbor.

Set the two equations equal to each other to find the x coordinate at which they meet, and then plug that into either equation to find the y coordinate.

Then, use your now point in combination with your previous point of (210,57) to find the distance between them.