a
Least count of screw gauge \(= \frac{{0.5}}{{50}}mm = 0.01mm\)
\(\therefore\) Reading \( = \,\left[ {Main\,scale\,\,reading + circular\,scale\,reading \times L.C} \right] - \left( {zero\,error} \right)\)
\( = \left[ {3 + 35 \times 0.01} \right] - \left( { - 0.03} \right) = 3.38\,mm\)