Supplementary angles are 2 angles with the sum of their measures being 180°. Each angle is called the 'supplement' of the other angle. If you know the measure of one of the angles you can find the measure of the supplement by one of 2 methods. Given the measure of one of the angles you can simply subtract it from 180°. Most people prefer to add rather than subtract and they prefer the next method which is to simply 'count up' to the next multiple of 10, then 'count up', by 10's, to 180°. Easy.
Consider your are given angle has a measure of 25°. The supplement can be found by subtracting it from 180°, as 180° - 25° which equals 155°. Using the other method, start with 25° and 'count up' to 30° (which is 5°) and then 'count up' by 10's to 180° (which is 150°). Since 5° + 150° = 155°.
In this problem set you will be given the measure of an angle and you will need to find the measure of the supplement. Use either method, striving for ease of accomplishing the problem and then strive for speed. Good luck and enjoy the challenge!