Answer:
Part A) The equation of the line m is 
Part B) The equation of the line n is 
Step-by-step explanation:
Part A) Line m has no y-intercept, and its x-intercept is (3, 0)
we know that
If a line has no y-intercept , then is a vertical line (parallel to the y-axis)
the equation of the line m is equal to the x-coordinate of the x-intercept
so

Part B) Line n has no x-intercept, and its y-intercept is (0, -4)
we know that
If a line has no x-intercept , then is a horizontal line (parallel to the x-axis)
the equation of the line n is equal to the y-coordinate of the y-intercept
so
