Answer:
r = 31.2
Step-by-step explanation:
Δ ACE and Δ BCD are similar, thus the ratios of corresponding sides are equal, that is
[tex]\frac{AE}{BD}[/tex] = [tex]\frac{CE}{CD}[/tex], substitute values
[tex]\frac{r}{19.5}[/tex] = [tex]\frac{64}{40}[/tex] ( cross- multiply )
40r = 1248 ( divide both sides by 40 )
r = 31.2
