From the law of sines, we have:

,
where x and y are the sides opposite to angles X and Y, respectively.
Substituting the known values, we have:

, thus

.
Using a calculator, we can find that arcsin(0.31)=18 degrees, approximately.
We know that sine of (180-18)=162 degrees is also 0.31. But 162 and 51 degrees add up to more than 180 degrees.
Thus, there is only one triangle that can be formed under these conditions.