Please help<3What is the length of SR?9 units12 units15 units18 units

From ΔRTQ :

    cos (RQT) = TQ / RQ = 16/20 = 4/5 = 0.8

∴ sin (RQT) = √(1-sin²(RQT)) = 0.6

∴ tan (RQT) = sin (RQT)/ cos (RQT) = 0.6/0.8 = 0.75  ⇒⇒⇒ (1)

But
   tan (RQT) = SR/RQ ⇒⇒⇒ (2)

From (1) and (2):

∴ SR/RQ = 0.75
∴ SR = 0.75 * RQ = 0.75 * 20 = 15
==============================================================
Another solution:
------------------------
∵ ΔSRQ is a right triangle
and RT⊥SQ

    RT = [tex] \sqrt{RQ^2 - TQ^2} [/tex]
∴ RT = [tex] \sqrt{20^2 - 16^2} [/tex] = 12
And
   RT² = ST * TQ
∴ ST = RT² / TQ = 12²/16 = 9
∴ SR = [tex] \sqrt{ST^2 + TR^2} [/tex]
∴ SR = [tex] \sqrt{9^2 + 12^2} [/tex] = 15
==============================================================
Another solution:
------------------------
∵ ΔSRQ is a right triangle
and RT⊥SQ

   RQ² = QT * QS
∴ QS = RQ²/QT = 20²/16 = 400/16 = 25

∴ SR = [tex] \sqrt{SQ^2 - RQ^2} [/tex]
∴ SR = [tex] \sqrt{25^2 - 20^2} [/tex] = 15