Looking at the quantities you have penciled in, you can expect to notice two things: First, two of the squares have the identical pair of quantities (and only all those two figures), and next, the four only appears the moment. Two of all those squares are previously penciled in with a matching pair of 5 and 6, so we know we can eradicate 5 and six as achievable options for the other boxes. Box six demands a 4.