A lamp-post PQ is 15m tall. A wire joins the top of the lamp-post P to a point R on the ground such that the wire makes an acute angle θ with the horizontal line QR. It is given that sinθ=135.
a. (i) Find cosθ.
b. (ii) Determine the length of the wire PR.
c. (iii) Calculate the distance QR between the foot of the lamp-post and the point R.