The three angles of a triangular flag are x, twice the complement of x, and one-half the supplement of x

Let x be the first angle
y be the second angle
z be the third angle.

for the second angle, complementary angles are angles sum are 90 degrees
y = 2 ( 90 - x )
y = 180 - 2x
2x + y = 180
for the third angle, supplementary angles are angles sum are 180 degrees
z = 0.5( 180 - x )
z = 90 - 0.5x
0.5x + z = 90

then the sum of a triangle is 180
x + y + z = 180
so x = 60
y = 60
z = 60