The areas of a triangle add up to 180 degrees. Therefore to tackle this question you must use algebra as you know that the sum of a, 2a and 2a + 30 is 180. a + 2a + 2a + 30 = 180 All the like terms can be put together; 5a + 30 = 180 Then to solve the equation now you can minus 30 from both sides; 5a = 150. And now divide both sides by 5 to get a on its own; a = 30.