In Fig. 10.103, a quadrilateral `A B C D` is drawn to circumscribe a circle such that its sides `A B ,\ B C ,\ C D` and `A D` touch the circle at `P ,\ Q ,\ R` and `S` respectively. If `A B=x\ c m` , `B C=7c m` , `C R=3c m` and `A S=5c m` , then `x=` (FIGURE) (a) 10 (b) 9 (c) 8 (d) 7