A slope is known as a rise/run or a rise over run
You can find the rise/run (slope) by finding the y-intercept on the graph (if it is on the graph which in this case it is the y-intercept is 5)
For example: if 3/4 was the slope then 3 would be the rise which means that you would move from the y-intercept upwards 3 points and 4 would be the run and would be move over to the right by 4 points. From the y-intercept you rise 3 points and run 4 points.
This graph is negative as noted by its downward direction meaning the slope will be negative.
To find the slope first find the y-intercept in this case y-intercept = 5.
Next find another solids point that also passes through the line, in this case this is point (1,3)
Move from the y-intercept (5) by -2 points or downwards by 2.
Then move over (run) by one point.
The -2 rises or in this case falls and the 1 goes to the right/runs
Insert these two numbers into the rise/run formula
-2/1 = -2
The answer is -2