The area of a triangle is calculated by: 1/2 of the base times the height.
That means that for your triangles, the base times the height can equal 20 cm2.
Since right triangles are the easiest to draw and label, you can draw a right triangle with a base of 5 and a height of 4 and another right triangle with a base of 10 and a height of 2.
All you need to do is draw the third side of the triangle (the hypotenuse).
Hopefully this was helpful!