Question 891534
{{{S=3C+10}}}
.
.
.

{{{S+A=180}}}
{{{C+A=90}}}
{{{S+A-C-A=180-90}}}
{{{S-C=90}}}
Substituting from above,
{{{3C+10-C=90}}}
{{{2C=80}}}
{{{highlight(C=40)}}}