Your dependent variable would be the degree of response in your test subject - the amount of anger/frustration felt. The independent variable would be the type and/or number of points in the instructions that were made to be "inadequate".
One way to increase the chances that the subject would feel anger/frustration is that they would be told they HAD to complete the task in a certain time frame by a person of "authority" (teacher, potential employer) or that they would be denied some type of reward (they would be paid some amount, but only if they complete the task in the time frame allotted).
Some other extraneous variables might be if they try to call someone for held (no cell phones allowed!), or if they were on anti-anxiety medication/drugs.