When an equation is in slope-interest form, y = mx + b, the 'm' indicates the slope of the line and the 'b' is the y -intercept. When you observe a graph of a line, you need to identify where the line crosses the y-axis. That is the 'b'. From that point, you identify another point the line crosses. From the y-intercept, determine the fraction formed by the vertical change and the horizontal change. That fraction is the slope, 'm'. If the line goes up to the right, the slope is positive. If the line goes up to the left, the slope is negative.
Observe the graph. Determine the slope, 'm' and y-intercept, 'b', then identify the equation of the line. Strive first to have high accuracy and then strive to increase your speed. Good luck and I hope you enjoy the challenge!