Question 53179
Let's start by detailing what we're representing:

angle = x
suplement = 180-x
complement = 90-x

{{{180-x = 2(90 - x) + 10}}}
{{{180-x = 180 - 2x + 10}}}
{{{2x - x = 180 - 180 + 10}}}
{{{x = 10}}}