Ok, so in order to have full-scale deflection w/ 20.0 V:
V = IR
20/(1x10^-3) = 20000 ohms (<--total resistance)
20000 - 60 = 19940 ohms for the resistor in series with the 60 ohm galvanometer.
Likewise, for 50 V the resistor would need to be 49940 ohm and for 100 V, 99940 ohm
I'm not sure...