Okay so my homework says the measures of two angles of a triangle are given. find the measure of the third angle

 
Do you remember hearing that the angles of every triangle in the world
all add up to the same number ?  They always add up to 180 degrees.

If you know the measures of two of the angles, then just take those away
(subtract) from 180 degrees, and whatever you have left must be the last angle.

For example, let's take the last one on your list:

54 and 36 are given.

       180 minus 54 = 126
then
       126 minus 36 = 90 . . ==> the missing angle is 90 degrees

Another way to do it:  One addition and one subtraction.

(54 + 36) = 90      That's the total amount you have to take away from 180.

180 minus 90 = 90  <== that's the missing angle.