I drew a graph representing 3 inequalities to solve this problem.
First, I sketched out a line y < (3/7)x which is our target. We want to know whether our point is below the line y = (3/7)x
From statement 1, I sketched out a line y < x - 4. You can see that the area below the line y = x - 4 is both above and below the line y = (3/7)x, depending on what value of x you pick. Thus, statement 1 is insufficient.
From statement 2, I sketched out a line y < (5/14)x. Again, the resulting area is either below or above the line y = (3/7)x, depending on the x value. Insufficient.
1&2 together, you can see that the area that are below BOTH lines y = x - 4 AND y = (5/14)x is ALSO below the line y = (3/7)x. That means, if you put constraints 1 & 2 together, the resulting value for y will always be less than (3/7)x. Hence, C.
