The angles must add to 180 degrees.
Since the angles are in the ratio 7:9:4, their measures are not 7, 9, and 4 since 7, 9, and 4 do not add to 180. If you multiply 7, 9, and 4 by the same number, the new numbers will be in the same ratio. Since we do not know what that number is, we can use x for it.
Multiply 7, 9, and 4 by x to get
7x, 9x, and 4x.
Now add them and set equal to 180.
Then solve for x.
7x + 9x + 4x = 180
20x = 180
x = 9
Now that we know x equals 9, substitute x with 9 and evaluate 7x, 9x, and 4x to find the actual angle measures.
7x = 7 * 9 = 63
9x = 9 * 9 = 81
4x = 4 * 9 = 36
The angles measure 63, 81, and 36 degrees.