There is often a need to produce more than one voltage from a single supply using a voltage divider. For example, the memory components of many personal computers require voltages of +12V, +5V and -12V, for example, all with respect to a common reference terminal. 

For the figure below, select the values of R1, R2 and R3 to meet the following design requirements;

a)  The total power supplied to the divider circuit by the 24V source is 120W when the divider is unloaded.

b)  The three voltages, all measured with respect to the common reference terminal, are V1 = 12V, V2 = 4V and V3 = -8V.