A) If voltmeter measures 2V across a 50 ohm resistor what current goes through the resistor?

B) The voltmeter itself has 10Mohm internal resistance; how much current goes through the voltmeter?
C) How much current should have gone through the Ammeter? Use the formula I actual = I of R +I of voltmeter. Is this a big error?

For first part I got 0.04A, second part I got 2 x 10^-7 A for voltmeter and 4.00002x10^-2 A. I think the calculations were done correctly but if not please let me know. But what I don’t understand is whether if this is a big error or not. By just looking at it I would say not because .00002 is relatively small but is that right way to look at it? Is there a formula I should use to clarify my point?

No, it is not a big error. You are analyzing it correctly.