[Twickel]

Hi
Attached is an image of eutetic phase diagram, how do I figure out the compositions at 200 degrees celcius, I tried for 180 but my answers did not match. First what I did was 50% mol ratio so first, draw a line from 200 degrees to match with 50 % ATOMIC Sn. Then since the question wants % WEIGHTS, do I connect the tie lines to the bottom axis if so then what.
Thanks