For a y-intercept, set in your equation. Remember that a y-intercept intercepts the y-axis, which is found at . Thus, setting will give you the place where your equation intercepts the y-axis.
For an x-intercept, do the opposite, set . This is because the x-axis is found at . Similar to the y-intercept, this will find you the point where your equation intercepts the x-axis.
She travels 1800 meters because the bus ride is moot point and she walks home twice once for lunch and once to come home for night and once back to work, so three times 600 meters is 1800 meters