the diagram shows a triangle. what is the value of c? c = □°

Explanation:

Step1: Recall angle - sum property of a triangle

The sum of the interior angles of a triangle is 180°. So, we have the equation $(c - 39)+91+(c - 28)=180$.

Step2: Simplify the left - hand side of the equation

Combine like terms: $(c + c)+(91-39 - 28)=180$, which simplifies to $2c+(91 - 67)=180$, and further to $2c + 24=180$.

Step3: Isolate the variable term

Subtract 24 from both sides of the equation: $2c+24 - 24=180 - 24$, resulting in $2c=156$.

Step4: Solve for c

Divide both sides of the equation by 2: $\frac{2c}{2}=\frac{156}{2}$, so $c = 78$.

Answer:

$78$