A triangle’s angles added up are 180 degrees and a triangle must have 3 angles, therefore the formula is: a + b + c = 180
So lets substitute the angles in your problem to the formula.
Let a = 25 degrees
Let b = 20 degrees
And let c = x + 144
25 + 20 + (x + 144) = 180
Add common variables, in this case 25 and 20:
45 + (x + 144) = 180
Isolate the x variable, first by subtracting 45 from both sides.
45 - 45 + (x + 144) = 180 - 45
x + 144 = 135
Now, subtract both sides by 144:
x + 144 - 144 = 135 - 144
x = -9
Your answer is: x = -9