Question 154692
The complement of angle x is 90° - x
The supplement of angle x is 180° - x.
So their average is
{{{((90 - x)+(180 - x))/2}}}
={{{(90 + 180 -2x)/2}}}
={{{(270 - 2x)/2}}}
={{{270/2 - (2x)/2}}}
={{{135-x}}}