Ok, I managed to get the last one.
Start the level, and press 'R'.
As soon as it restarts click the left pink square. Now wait for the yellow ball to get under the brown ball slightly, and drop the brown ball onto it. hopefully, the original yellow ball is knocked back towards the left and the original brown ball goes to the right.
If 17 is the one I'm thinking of... let the first yellow one go, and let it go down and hit the brown one. Then let the next small yellow one go, and it will roll down that slope... Then relase the big one and it should launch it over the wall...