Basic DC series question

Hello everyone
I'm just getting ready for level 1 electrical exemption exam.
Someone suggested the following awnser to the following problem.
See picture attached. If ground is attached to (+) of the 36V source wouldn't that have adverse affect?
Why do you substract 24v from the 36v?

Please help me understand this ?
The awnser is also showing -12V

You need to apply Kirchhoff’s Second Law to find the current and then use it to find the voltage difference between Va and Vg.

https://www.miniphysics.com/using-kirchhoffs-laws-on-a-single-loop-circuit.html

Grounding gets a little complicated sometimes. In this case, think of it as a reference point.

Putting a ground between two supplies like that will create some 'positive' voltage (above the ground point) and 'negative' voltage (below the ground point) because you are referencing to ground.

-12V is right for me.

The two batteries in series give 48V therefore each group of 2 resistors has a voltage drop = 24 V, so the difference between point A and ground will be 12V -24V = -12V, and if you calculate it in the other direction it will be 24V - 36V = -12V