1. This level requires you to balance the scale with the items.
First, find the two hidden objects.
One is in the light above the door.
Drag it down (for iOS, shake your phone).
The second item (sled) can by found by tilting your phone/device to the left.
2. Now put the items one by one onto a scale to see how much it weighs, then balance it.
Put the following items on the left scale: Sled/3kg weight/blue weight
Put everything else on the right scale.