On circle O below, SE is a diameter.
What is the measure of ISE

Angle LIS is congruent to angle DIE making both of them 61°, angle LID and angle SIE are congruent as well. When you add LIS, DIE, LID, and SIE all add to 360°. So 61+61 equals 122. 360-122 is 238. You divide 238 by 2 to get 119. That will be the measure of angle SIE. A triangle is a total of 180° so add up the angles 27° + 119° to get 146°. Subtract that from 180° to get 34°.

34° is the measure of ISE

Hope this helps!