Isaac physics C4a.2 - struggling

Link to the question: https://isaacphysics.org/questions/phys19_c4a_q2?board=phys19_c4_add&stage=a_level.
For the second part of the question, it asks to find In terms of V the potential difference of the parallel circuit. I thought the answer would just be V as potential difference is the same in parallel circuits. But it says that's the potential drop of the whole circuit. Help would be much appreciated.

Did you take into account the "top" resistor which is in series with the two parallel branches.

I tried figuring out how to use that but I don't see how I could use any of the laws in order to find its "V value".