>>45980363The numbers on the left and bottom tell you how many Voltorb cards are in each line/column and the sum of the numbers on the non-Voltorb cards.
From that, you can deduce which cards are safe to flip and which aren't. Note that you only need to find the 2 and 3 cards.
So for instance, the red line that has 1 Voltorb and and a sum of 4 doesn't need to flipped at all, because it only contains 1 cards.
