Question 970496
{{{A+S=180}}}
{{{A+C=90}}}
{{{S=3C}}}
Substituting,
{{{A+3C=180}}}
{{{A+C=90}}}
Subtracting,
{{{A+3C-A-C=180-90}}}
{{{2C=90}}}
{{{C=45}}}
{{{S=3(45)=135}}}
{{{A+45=90}}}
{{{A=45}}}