geometry

Step - by - step:

Sum of angles in a triangle = 180

23 + 54 + x = 180

 

then  x + 'angle next to it' = 180

 

then 'angle next to it' + 36 + 'angle next to y'  = 180

 

then ' angle next to y'   +  y = 180                  <------ solve for y