Question 707143
Two angles are supplements when they add up to 180

Equation 1: {{{A + B = 180}}}
Equation 2: {{{A = B + 30}}}
-----------------------------
Plug (B + 30) into equation 1 for A
Equation 1: {{{A + B = 180}}}
{{{(B + 30) + B = 180}}}
Combine like terms
{{{2B + 30 = 180}}}
Subtract 30 from both sides
{{{2B = 150}}}
Divide both sides by 2
{{{highlight(B = 75)}}}
Now plug 75 into equation 2 for B
Equation 2: {{{A = B + 30}}}
{{{A = (75) + 30}}}
{{{highlight_green(A = 105)}}}