Original circuit: ER = 55 volts ; IR = 11 A
With 7 amp current source only: ER = 35 volts ; IR = 7 A
With 4 amp current source only: ER = 20 volts ; IR = 4 A
35 volts + 20 volts = 55 volts
7 A + 4 A = 11 A
Notes:
This circuit is so simple, students should not even require the use of a calculator to determine the current figures. If students are not familiar with current sources, this question provides an excellent opportunity to review them. The main point of the question is, however, to get students to see the concept of superposition of voltages and currents.