I'm sorry if I get this wrong, but there isn't enough evidence.
If we think about the shorter side being 4.2 cm, then just divide 33.6 by 4.2 to give it a ratio. 33.6 / 4.2 is 8. The ratio of the scale drawing to the actual playground would be 1 : 8.
The longer side is 10.5, so just multiply that by 8. You'd get 84 meters. The only part left is getting the area.
Multiply 84 x 33.6 and you'd get 2822.4
The answer would be 2,822.4 squared.