P is a point inside a rectangle ABCD, where PA = 3, PC = 7 and PD = 6. Find PB.
Because PA=3 and PC=7, the diagonal AC=10. Since ABCD is a rectangle, it is also a parallelogram. Since ABCD is a parallelogram, segment AB ≅ segment DC because opposite sides of a parallelogram are congruent. Therefore PB=10-PD= 10-6=4.
The answer is 4.