\(9 \text { M.S.D }=10 \text { V.S.D }\)
\(\text { 1 V.S.D }=0.9 \text { M.S.D }=0.9\,mm\)
\(\text { L.C of vernier caliper }=1-0.9=0.1\,mm =0.01\,cm\)
\(\text { zero error }=-(10-4) \times 0.1\,mm =-0.6\,mm\)
\(\text { Reading }=\text { M.S.R }+\text { V.S.R }-\text { Zero error }\)
\(=3\,cm +6 \times 0.01-[-0.06]\)
\(=3+0.06+0.06\)
\(=3.12\,cm\)
Nearest given answer in the options is \(3.10\)