Hello and Good Morning/Afternoon
Let's take this problem step-by-step
The Line DF is '5x + 7' cm long
The Line DF is made up of two lines DE and EF
⇒ therefore
[tex]DE + EF = \\ 7 + 4x + 3 = 5x + 7\\10+4x=5x+7\\5x-4x=10-7\\x=3[/tex]
Let's plug x's value into '5x + 7'
[tex]\hookrightarrow DF = 5(3) +7=22[/tex]
Answer: 22cm
Hope that helps!
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