I believe the answer would 5 blocks
If you go 3 blocks East and 4 north, they are like the straight sides of a triangle, so to find the diagonal distance, or the shortest distance, you would find the diagonal side of a triangle it is
A squared + B squared = C squared
So 3x3 = 9
And 4x4 = 16
16+9=25
And the square root of 25 is 5
Please correct me if I am wrong and have a good day