Shadow of the tomb raider - Child Lara memories

During shadow of the tomb raider you are transported back to young Lara Crofts memories of her as a kid in the playground.
Within the playground there is a chest located in the crows nest on the ship. In order to gain this chest you need to aim and throw the weights which are dotted around the ship in order to weight it down enough for young Lara to reach it.
3 weighted balls are required to complete this challenge.