Let QR = 4 + x
Let the radius of the larger circle be PM
Let the radius of the smaller circle br QN
We can construct similar triangles PMR and QNR such that
PR / PM = QR / QN
( 13 + x) / 5 = (4 + x) / 4
4 (13 + x) = 5 (4 + x)
52 + 4x = 20 + 5x
x = 32
QR = 4 + 32 = 36
+0 
