I think your answer is right and it also can be written as :
Plot the points A = (4,0), B=(4,5), C=(0,7), and D= (0,0).
Write a series of simultaneous inequalities that describe the region enclosed by the quadrilateral ABCD formed by the joining four points.
My answer is y > or equal to 0
x > or equal to 0
x < or equal to 4
y < or equal to -1/2x + 7
is my answer correct?