Referring to the example combining series and parallel circuits and Figure 21.6, calculate I3 in the following

Question:

Referring to the example combining series and parallel circuits and Figure 21.6, calculate I3 in the following two different ways:
(a) From the known values of I and I2;
(b) Using Ohm's law for R3. In both parts explicitly show how you follow the steps in the Problem-Solving Strategies for Series and Parallel Resistors.