A screw gauge has a pitch of 1 mm and 100 divisions on its circular scale…

Step 1. The least count. $\text{LC} = \dfrac{1\ \text{mm}}{100} = 0.01$ mm.

Step 2. The zero error. The closed reading is close to 100, so the error is negative: $-(100 - 94) \times 0.01\ \text{mm}$ $= -0.06$ mm.

Step 3. The metal sheet. Observed: $3\ \text{mm} + 42 \times 0.01\ \text{mm}$ $= 3.42$ mm. Corrected: $3.42\ \text{mm} - (-0.06\ \text{mm})$ $= 3.48$ mm.

Step 4. The stack. Observed: $1\ \text{mm} + 11 \times 0.01\ \text{mm}$ $= 1.11$ mm. Corrected: $1.11\ \text{mm} + 0.06\ \text{mm} = 1.17$ mm.

Step 5. One sheet of paper. $\dfrac{1.17\ \text{mm}}{20} = 0.0585$ mm.