5 1 .. . . . . 7 .	7 9 3 1 6 8 . . .	.. 4 .. . . 7 3 1 9
.. 8 7 . . 3 . . .	9 .. .. 6 7 4 .. .. ..	. . . . . . 4 7 2
. . . 7 4 9 . . .	3 2 7 . . .. . . .	. . . . . . 7 8 6
In the second block, 7 can not be in the lower row because of the 7 in the left block. It can not be in the middle row because it is full. Thus it has to be in the upper row. There, it can not be in the third column because in the lower block there is already a 7 in that column.
The digits 7 rule out every other spot in the block.
3 can not be in the lower row because of the 3 in the right block. This gives us one possible spot in the block.