AREa of a triangle!?!?! Plz help?!?!??!?!?!?

I saw and it said multiply the base tiimes the height and I don't know how to find the base but here's the dimensions...it Iz a triangular pyramid... The bottom sides are each 4 cm the alan hieght is 5 cm and the height is 4cm!!! I need the base, what is it?