the numbered balls indicate at what point those disappear when you match the number to the number of balls in the same row or column it is in. Obviously, the 7 only happens on a full row or column. The tutorial needs to do a better job at explaining it.
Driving on the grass doesn't reduce speed and the oil slicks don't really hinder you. Hitting the wall doesn't slow you down and neither does going straight through trees. 3/5