The 1A DC current source on the left actually forms an effective loop, that is, through an 8-ohm resistor, the voltage is 8V, and it is -8V from A up.

The middle 5V voltage source does not form a loop. In fact, the resistance of 10 ohm above has no current (in the case of ideal voltage source and current source), and the voltage here is 5V.

The effective loop formed by the 3V voltage source on the right is a 6 ohm and 9 ohm series circuit.

The voltage between ab (from point A to point B) =8 ohm resistance voltage +5V voltage source voltage +6 ohm resistance voltage.

A voltage drop is a voltage drop. When the voltage rises in the current direction, it means rising. When it is opposite to the current direction, it is generally called voltage drop (whether it is rising or falling).

As long as it is clear that the current loop on the left is clockwise and the current loop on the right is counterclockwise, can you calculate the voltage and current?