The equation representing the straight line graph with a y-intercept of 9 and a slope of 3 is y = 3x + 9.
The question seems to be referring to the representation of a straight line graph and which equation corresponds to it.
The key information is that the line graph has an y-intercept of 9 and a slope of 3.
Therefore, the equation that represents this straight line graph would be y = 3x + 9, which follows the standard format of a linear equation in slope-intercept form, y = mx + b, where m is the slope and b is the y-intercept.