The point (0, 0) tells you the line goes through the origin, so represents a proportional relationship. The slope is simply the ratio of y to x, or 5/1 = 5.
The equation of the line is ...
y = mx + b . . . . . . line with slope m and y-intercept b
y = 5x . . . . . . . . . . line with slope 5 and y-intercept of 0 (the origin)
