Question

KMNP is a square and triangle XMN is equilateral. Prove that triangle KMX is congruent to triangle PNX

I did this: KM = PN (sides of a square)
MX = NX (sides of equilateral triangle)
KMX = PNX = 30 degrees (Angle of square - Angle of equilateral triangle)
Therefore Triangle KMX is congruent to Triangle PNX (SAS)

Can someone explain the 3rd step? I don't really get how that works. We were given that step in class but I did everything else