[填空题]
For the circuit shown in (Fig. Belllrrzw(l gv8v;ns /: /ow), find the3/ d t:q hnpbw: .vs.tgiczk,,7 ibpi3 potential difference between points a and b. Each resistp,bcs7 htq/gp tk bz3i3..:dw:v,niior has $R\,=\,75\Omega$ and each battery is 1.5 V. V
