the diagram shows a triangle.\nwhat is the value of a?\na = \\square^\\circ

Explanation:

Step1: Recall triangle angle sum

The sum of angles in a triangle is (180^\circ). So, (12a + 42 + 30 = 180).

Step2: Simplify the equation

Combine like terms: (12a + 72 = 180). Subtract 72 from both sides: (12a = 180 - 72 = 108).

Step3: Solve for (a)

Divide both sides by 12: (a = \frac{108}{12} = 9).

Answer:

(a = 9)