Question 168318
lets call the angles a,b,and c

a+b+c=180  eq 1

b=2a.......eq 2
c=b+30.....eq 3

plug b's value from eq2 and c's value from eq 3 into 1st equation

a+(2a)+((2a)+30=180

5a+30=180
5a=150
{{{highlight(a=30)}}} 
{{{highlight(b=2(30)=60)}}}
{{{highlight(c=60+30=90)}}}