If angle D is congruent to angle E, then the triangle DFE is an isosceles triangle (look at the picture).
Therefore DF ≅ EF.
DE = x + 4, EF = 4x - 8, DF = 7x - 35
The equation:
7x - 35 = 4x - 8 add 35 to both sides
7x = 4x + 27 subtract 4x from both sides
3x = 27 divide both sides by 3
x = 9
DE = x + 4 → DE = 9 + 4 = 13
EF = 4x - 8 → EF = 4(9) - 8 = 36 - 8 = 28
DF = 7x - 35 → DF = 7(9) - 35 = 63 - 35 = 28
Answer:
x = 9, DE = 13, EF = 28, DF = 28.
