Answer:
DE = 21
Explanation:
Recall: the ratio of the corresponding side lengths of similar triangles are equal
Given that ∆ABC ~ ∆DEF, therefore,
AB/DE = BC/EF = AC/DF
AB = 8.4
DE = x
BC = 10
EF = 25
AC = 16.5
DF = 41.25
Let's find DE using AB/DE = BC/EF. Thus:
8.4/x = 10/25
Cross multiply
x*10 = 25*8.4
10x = 210
Divide both sides by 10
x = 210/10
x = 21
DE = x = 21