Answer:
[tex] \frac{ae}{be} = \frac{ce}{de} = \frac{bc - be}{ad - ae} \\ \\ = > \frac{8}{3} = \frac{15 - 3}{ad - 8} \\ \\ < = > \frac{8}{3} = \frac{12}{ad - 8} \\ \\ = > ad - 8 = \frac{12 \times 3}{8} = 4.5 \\ \\ < = > ad = 4.5 + 8 = 12.5 \\ \\ = > r = 12.5 \div 2 = 6.25[/tex]
