The upper and lower fields on level 75 are technically inverted. Thanks to the portals, pieces can travel from the bottom of the lower field to the upper one. In order to collect the Acorns you will need to either reach the upper field with explosions or use the Rainbow Blast on Berries. Collect as many firecrackers and bombs on the field and explode them together — it will fill up your Rainbow Blast meter faster, and thus save you moves to collect Acorns. Don’t worry if you have to spend a few moves in the beginning — as soon as you get access to the upper field, you will start clearing the field way quicker.