Find the area of triangle whose adjacent sides are along vectors 3j and 5k ?

Let the triangle be ABC
So AB = 5k, BC = 3j
Area of a triangle is half of the parallelogram.

So Area of the parallelogram having sides AB and BC is AB $\times$ BC
AB X BC =
So AB X BC = -15i
|AB X BC| = 15
So area of triangle will be 15/2 = 7.5 units