[tex] \sqrt{210} [/tex]
There is a theorem in Geometry stating that the square of the tangent segment (ST) is equal to the product of the external secant segment (TR) and the whole secant segment (TQ).
SQ x SQ = TR x TQ
SQ squared = 7 x 30
SQ squared = 210
SQ = [tex] \sqrt{210} [/tex]
