We create equations and solve for the length*
Let X be 1 side of length, Y be the other side of length,
Then:
X * Y = 40
X = 40/Y ----(1)
2X + 2Y = 26 ---- (2)
Sub (1) into (2):
2 (40 /Y) + 2Y = 26
80 + 2Y^2 = 26Y
2Y^2 - 26Y + 80 = 0
Y^2 - 13Y + 40 = 0
(Y - 5)(Y - 8) = 0
Y = 5 or Y = 8
Then X = 8 or X = 5
:. Vertical length is 5/8cm,
Horizontal length is 8/5cm.

From (-3,-5):
Since origin within rectangle,
The diagonal point is at the top right,
:. (-3 + 5, -5 + 8)
= (2,3)
OR (-3 + 8, -5 + 5)
= (5,0)

(2 possible rectangle, longer vertical or horizontal, hence there are 2 possible points, 1 per rectangle)