The distance between D and E is 5 units and the area of a triangle is:
A=bh/2 if we let DE be the base and A=15 we have
15=5h/2
5h=30
h=6 (there are actually infinitely many solutions to create this height of 6 units high away from the base)
The simplest four are the right triangles formed when F is either:
(2,7), (2,-5), (7,7), and (7,-5)