this one is a bomb....i go with E...
the 2 conditions do not agree as per ian777's GMAT ideology...
Thanks for reading my posts. I'm glad you're taking this to heart, because it is an important point. The two statements in a DS do have to agree.
In this case, though, I think they do. There are 3 variables, x, y, and z, and so we need to have three equations. We get one from the question: z=5x.
Statement 1 gives us another one: 5x + 3y + z = 60.
Statement 2 gives us the third: 2y = x
If you put them all together, you can solve for x (although the answer is certainly not an integer answer - but the question never said it had to be).
So I get C, also.
How did you see it?