How to find the shorter diagonal of a parallelogram?

Hello, I am an 8th grade geometry student and I am stumped here. I have a parallelogram here. Using only the shorter side length of 12 centimeters, the longer side length of 15 centimeters, and the obtuse angle between them of 118 degrees, find the length of the shorter diagonal. I have been racking my brain for hours here. I can't use the law of cosines, because it only applies to the longer diagonal. I need the shorter diagonal, and I don't have an angle measure for it. I am stumped. How would I solve this? I used the L.O.C. and found that the longer diagonal is 23.19 degrees approximately, if that is of any help.