Final answer:
The y-intercept is the value where a line crosses the y-axis when x=0, indicated by the constant term b in the equation y=mx+b.
Step-by-step explanation:
The y-intercept of a linear equation is the value of y when x is equal to zero. It is represented by the value b in the slope-intercept form of a linear equation, which is y = mx + b, where m represents the slope and b indicates the y-intercept. In given line equations like y = a + bx and y = 55x + 75, the y-intercept would be the constant a or 75 respectively. Additionally, in terms of a figure where the line graph is shown, the y-intercept would be explicitly marked, such as the point where the line intersects the y-axis being 9.