I’ve studied vectors but I can’t do this question in a book.

PQRS is a rhombus of side 4 units. K, L, M and N are the mid-points of PQ, QR, RS and SP, respectively. SN® is a representative of vectoruand SM® a representative of vectorv. Show that SK®.SL® = 5u.v+ 16.

The rhombus has P at the top left corner and S directly below. Q is slightly lower than P and R is directly below Q.