Math Smashers

when I reach level 41, the goal is 37, and there is nothing I can do to kill the circle with 37 -.- Don't have any negative number, and dies when combine with anything else :P please fix it

The targets are on layers and it's difficult to see what's being selected, often leading to death. The concept is great and most of the execution is flawless, but how the targets are selected needs work. The limited lives seems like an unnecessary constraint.