How to tell if an equation is independent dependent or inconsistent?

The example for an inconsistent system of equations:
x + 2 y = 10 and x + 2 y = 20. If we try to solve it algebraically:
x = 10 - 2 y; 10 - 2 y + 2 y = 20; 10 = 20 ( not true ). We will with something that is not true. Graph of those equations shows 2 parallel lines. Therefore the system is inconsistent.
The system is dependent when we have equivalent equations. For example:
2 x + y = 5 and 4 x + 2 y = 10. If we try to solve this system, we will end up with: 0 = 0 ( true ). The graph of this system shows the same line. This system is dependent.
Finally, if we have just one solution for the system of equations then the system is independent. For example: x + y = 5 and  - x + 2 y = 10. When we add those equations: 3 y = 15; y = 15 : 3; y = 5; x + 5 = 5; x = 0. So we have just one solution ( x , y ) = ( 0, 5 ). The system of equations is independent.

The answer would be 13.5 minutes.