Question 59256
You have 3 unknowns
That means you need 3 equations, or you can't solve.
The one you're missing is:
a + b + c = 180 That's true of all triangles
[1]{{{b = a + 6}}}
[2]{{{c = 3*(a + b) - 4}}}
[3]{{{a + b + c = 180}}}
expand [2]
{{{c = 3a + 3b - 4}}}
subtract c from both sides
[4]{{{3a + 3b - c - 4 = 0}}}
add 4 to both sides
{{{3a + 3b - c = 4}}}
multiply both sides of [3] by 3
{{{3a + 3b + 3c = 540}}}
subtract one from the other
{{{4c = 536}}}
{{{c = 134}}}
substitute in [4]
{{{3a + 3b - 134 -4 = 0}}}
[5]{{{3a + 3b = 138}}}
[1]{{{b = a + 6}}}
{{{a - b = -6}}}
muiltiply both sides by 3
{{{3a - 3b = -18}}}
add to [5]
{{{6a = 120}}}
{{{a = 20}}}
[3]{{{a + b + c = 180}}}
{{{20 + b + 134 = 180}}}
{{{b + 154 = 180}}}
{{{b = 26}}}
check
[1]{{{b = a + 6}}}
{{{26 = 20 + 6}}}
{{{26 = 26}}}
[2]{{{c = 3*(a + b) - 4}}}
{{{134 = 3*(20 + 26) - 4}}}
{{{134 = 3*46 - 4}}}
{{{134 = 138 - 4}}}
{{{134 = 134}}}
OK
so,
a = 20 degrees
b = 26 degrees
c = 134 degrees