Answer:
RT = 18
Explanation:
given 2 secants to a circle from an external point, then
the product of one secant's external part and that entire secant is equal to the product ot the other secant's external part and that entire secant, that is
RS × RT = RQ × RP
11(11 + x) = 9(9 + 13)
11(11 + x) = 9 × 22 = 198 ( divide both sides by 11 )
11 + x = 18 ( subtract 11 from both sides )
x = ST = 7
Then
RT = RS + ST = 11 + 7 = 18