A galvanometer with a coil resistance of 40.0 W deflects full scale for a current of 2.0 mA. What series resistance should be used with this galvanometer in order to construct a voltmeter that deflects full scale for 50 V?

Kirchhoff's junction rule: At any junction point, the sum of all the currents entering the junction must equal the sum of all the currents leaving the junction.
Kirchhoff's loop rule: The sum of the changes in potential around any closed path of a circuit must be zero.