Greetings from Brasil....
Looking at the figure we can say that:
DF = DE + EF
DF = 9X - 39
DE = 47
EF = 3X + 10
inserting these data in the 1st expression....
DF = DE + EF
9X - 39 = 47 + (3X + 10)
9X - 39 = 47 + 3X + 10
9X - 3X = 57 + 39
6X = 96
X = 96/6
X = 16
EF = 3X + 10 anb X = 16, so
EF = 3·16 + 10
EF = 48 + 10
EF = 58
