Determining current through a short circuit
Let's try a way:
You could simplify R1 and R3 as they are two resistors in parallel.
You could simplify R2 and R4 as they are two resistors in parallel.
Do you agree the circuit would overall be equivalent ? Once you do that you can calculate the voltage on the short-circuit wire.
Then, go back to the circuit with the original resistors. You have the voltage at the mid point. You can probably do it from there.
Post you final answer, we'll verify it. :-)