With the legends barely readable, it is difficult to be conclusive. But, there aren't that many siliquas with the inscription "VOTIS X MVLTIS XX", so that narrows it down to three possibilities (OCRE link http://numismatics.org/ocre/results...3;xx&lang=en
1: Julian the Apostate, 361-363, mint Antioch
2: Valens, 375-378, mint Aquileia
3: Gratian, 375-378, mint Aquileia
From the partly readable inscriptions it can be narrowed down further:
- I think the mint mark (bottom of the reverse) reads AQP, possibly AQPS with just the top of S visible. That points to Aquileia. I can't read it as ANT, which it would have to be for Antioch. So it should be number 2 or 3. In addition, Julian should be portrayed with a beard, Valens and Gratian are not, and although I cannot say for sure, I don't think the OP coin has a beard.
- For Valens, the obverse inscription to the right of the head should read S P F AVG. I think it looks more like NVS P F AVG, which points to Gratian.
So I would say it is number 3, Gratian. The only concern is the inscription to the left of the head, which should read D N GRATIA. That is hard to make out, but perhaps with the coin in hand it is easier to see if that can be a match.