The y-intercept of a graph
Given the graph of a function, the y-intercept is defined as the y-coordinate of the point(s) where the graph crosses the y-axis.
There might be more than one y-intercepts or even none.
The graph provided in the question is a line with a negative slope, i.e., a decreasing line.
Carefully looking it can be determined the graph touches the y-axis in the point (0,-3), thus the y-intercept of the graph is y=-3