Using cosine theorem: the formula is COSC = (A+B-C)/2AB.

Cos 150 degrees =√3/2

When 600 is the longest side, that is, the opposite side of an obtuse angle (big angle versus big side), there is an equation √ 3/2 = (400+b-600)/(2 * 400 * b).

Get b=400√2-200√3.

600 is either the longest side or the side with an obtuse angle. Then there is the equation:

√3/2=(400^+600^-c^)/(2*400*600)

C=200√( 13+6√3)