When you say two angles are complementary, they add up to 90 degrees.
Since two angles are the ratio 2:7, you can represent the smaller angle as 2x and the larger as 7x.
add them up as 2x+7x=90
2x+7x=9x 90/9x=10x
the angles are 2x=20 degrees and 7x=70 degrees
so the smaller angle is 20 degrees
