Question 343337
BY DEFINITION THE SUM OF SUPPLEMENTARY ANGLES IS 180 DEGREES!
{{{S[1]+S[2]=180}}} 
THE QUESTION STATES THE FOLLOWING TO BE TRUE:
{{{S[2]= 3.5(S[1])}}}

SUBSITUTE
{{{S[1]+ 3.5(S[1]) =180}}}
CONVERT DECIMAL TO SIMPLE FRACTION
3.5 = 3 1/2 = 7/2
{{{S[1]+ (7/2)(S[1]) =180}}}
SIMPLIFY: MULTIPLY EACH TERM IN THE EQUATION BY 2
{{{2(S[1])+ 7(S[1]) =360}}}
COMBINE
{{{9S[1]=360}}}
SOLVE:
DIVIDE EACH SIDE OF THE EQUATION BY 9
{{{S[1]=highlight(40)}}} 
{{{S[2]=(7/2)(40)}}} 
{{{S[2]}}}= {{{highlight(140)}}} 

CHECK YOUR ANSWER!!  40 + 140 = 180