So the width can be written as W=3L-6. (L is length and W is width). The maximum the width could be is 45mm, so try to use 45mm in place of W. 45=3L-6. Add 6 to both sides and you get 51=3L. Divide both sides by 3 and you get 17=L, where L is the length.
The answer is D. Easy way to tell, the less than or equal to sign indicates a solid line in the graph. Equal=solid line. Also when you solve for y, the slope of the line (-2/3)is negative, indicating a line sloping downward.
