Answer
a=2 or 9
EC=3 or 24
Work Step by Step
$\frac{AD}{AE}$=$\frac{DB}{EC}$
$\frac{5}{a+1}$=$\frac{a+3}{3(a-1)}$
15a-15=a^$2$+4a+3
a$^2$-11a+18=0
(a-2)(a-9)=0
a=2 or 9
EC=3a-3
EC=3 or 24
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