Nodal Analysis: Resistor in front of Node A
Can you provide the entire circuit? Otherwise it would be impossible to help you.

Edit: ok

You know the current in the 10 Ohm resistor (it's 3A). You know the voltage accross the 20 Ohm resistor (it's 5V). So you can compute i with kirchoff current law (it will depends on VA because current in the 5V battery will be shared at VA).

From i you can compute the voltage accross the 100 Ohm resistor. Then by using kirchoff voltage law, you can easily find VA.

Here with formulas: