geometry
posted by Christopher .
in a triangle DEF m<E is three times m<,and m <F is 9 less than m< E

D = X deg.
E = 3X,
F = 3X  9.
X + 3X + (3X  9) = 180deg.
7X = 180 + 9,
7X = 189,
X = 189 / 7 = 27deg.
D = X = 27deg.
E = 3X = 3*27 = 81deg.
F = 3X  9 = 3*27  9 = 72deg.