Allocating resource split to task

Sorry Noob here. I want to create a task with two resources assigned to it. Task A will have 6 hours of a principals time with two hours of an assistants time. For a total of 8 hours of effort for the task split @ $200/hour for the principal and $115/hour for the assistant. When I assign two resources to the task it divides the effort at 4 hours each. Playing with the percentage affects the entire project vs just the task in question. How do I do this?

I would really like to know the answer to this question as well. I would like to have one task with 2 resources that work a set amount of hours on the one task at different pay rates. The only way I can see to change the amount of hours is by changing the unit percentage which does not give me an accurate cost amount per resource or total of resources together. Can the units be changed to hours instead of a percent?