Step-by-step explanation:
Given that,
DE = 8x - 13
EF = 5x + 17
DF = x + 21
Also,
DE = EF
which means that,
8x - 13 = 5x + 17
8x - 5x = 17 + 13
3x = 30
x = 30/3
x = 10
Now,
DE = 8x - 13 = 8×10 - 13 = 80 - 13 = 67cm
EF = 5x + 17 = 5×10 + 17 = 50 + 17 = 67cm
DF = x + 21 = 10 + 21 = 31cm
