Recall that the y-intercept is when the function passes the y-axis. This happens when x=0. Therefore, we can find our y-intercept by plugging x=0 into our function and solving for y.
6x + 9y = 18
6(0) + 9y = 18
0 + 9y = 18
9y = 18
y =2
Thus, our y-intercept is when x = 0 and y = 2, or (0,2).