Given a certain angle [tex] x [/tex], its complement is [tex] 90-x [/tex] and its supplement is [tex] 180-x [/tex].
So, if the supplement of an angle is 10 more than twice the complement, you have
[tex] 180-x = 2(90-x)+10 [/tex]
expand the right hand side:
[tex] 180-x = 180-2x+10 [/tex]
We can simplify the 180 appearing on both sides:
[tex] -x = -2x+10 [/tex]
Add 2x to both sides
[tex] x = 10 [/tex]
