We can imagine drawing a line over the dots that somehow approximates the dots (a trend line or line of best fit). The line would go from top left to bottom right so downhill. Mathematically it would have a negative slope so the correlation coefficient is negative.
Next remember that the correlation coefficient is a number from -1 to 1. At 0 the dots are everywhere and no real line can be drawn. The closer it is to 1 or -1 the more the dots look like a line.
These look pretty close to a line so the correlation coefficient is close to -1.
The answer, therefore, is -.8
