d: 90, because it is equal to the angle next to it. They are both right angles, and add up to 180 degrees: a straight line.
e: 81, as it is the corresponding opposite.
f: 99, as there are two 81-degree angles. These two angles add up to 162. A full circle is 360 degrees, so if you subtract 162 from 360, you will get 198. 198 divided by 2 (since there are 2 even corresponding angles) is 99 degrees.
