Answer:
r = 6
Step-by-step explanation:
Using Pythagoras' identity in the right triangle
PR² = PQ² + QR² , substitute values
(r + 4)² = r² + 8²
r² + 8r + 16 = r² + 64 ( subtract r² from both sides )
8r + 16 = 64 ( subtract 16 from both sides )
8r = 48 ( divide both sides by 8 )
r = 6
