B. 15ft
using similarity theorem of triangle
BE/DE = BC/AC
BE = 10
DE = 4.8
BC = 10 + x
AC = 12
so,
10/4.8 = 10 + x/12
2.083 = 10 + x/12
2.083 x 12 = 10 + x
25 = 10 + x
x = 25 - 10
x = 15ft
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