We really can't help you without knowing how the tolerances of the resistors and meters are specified. This sounds like a homework problem. You are better off consulting your textbook.
At first I thought it might be something to do with how the meter's resistance affects it's readings. However that can only cause the reading to be too low.
In this case the actual voltage across the 10K resistor is 3.83V, and he's talking about meter readings of 5V and 5.4V. In that case either the meter's broken or someone doesn't know how to use it.
Anyway, back to the questions...
A. If a voltmeter is connected to the 10K resistor and the voltmeter reads 5V on a 0-100V range. What is the sensitivity?