Question 651095
The sum of adjacent angles must 
add up to 180 degrees
given:
Let {{{ a }}} = the unknown angle
{{{ a = 2*( 180 - a ) - 15 }}}
{{{ a = 360 - 2a - 15 }}}
{{{ 3a = 345 }}}
{{{ a = 115 }}}
{{{ 180 - a = 180 - 115 }}}
{{{ 180 - a = 65 }}}
The angles are 65,65,115 and 115
checvk:
{{{ 2*65 + 2*115 = 360 }}}
{{{ 130  + 230 = 360 }}}
{{{ 360 = 360 }}}
OK