Which factors contribute to psoriasis? Select all that apply.
genetics
abnormalities of the immune system
seasonal changes
stress
hormonal changes

The price for each instructor will be the same at 3 hours. How I determined this

First off, you need to add the initial price and hourly price for each person together, so you already know how much it will cost for 1 hour, including the initial fee. Here's how you do it:

Ieda: $11.00 (hourly price) + $8.50 (initial fee) = $19.50 (for 1 hour)

Thanh: $10.50 (hourly price) + $10.00 (initial fee) = $20.50 (for 1 hour)

Now that you have the price for 1 hour including the initial fee, now you need to find the price for each hour after that. Here's how I did that:

I created a graph that looked like this:

Hours:       1                 2                  3               
Ieda:      19.50          30.50         41.50
Thanh:   20.50          31.00         41.50

Here's how I figured out the price for each hour:

Ieda:

Hour 1 (including initial price):
            $11.00 + $8.50 = $19.50
Hour 2 (excluding initial price): Only add the hourly price after Hour 1!
            $19.50 + $11.00 = $30.50 
Hour 3 (excluding initial price):
            $30.50 + $11.00 = $41.50

Thanh:

Hour 1 (including initial price):
            $10.50 + $10.00 = $20.50
Hour 2 (excluding initial price):
            $20.50 + $10.50 = $31.00
Hour 3 (excluding initial price):
            $31.00 + $10.50 = $41.50

So, looking at the graph, their prices are the same once each instruction reaches 3 hours. ($41.50)

I hope I was able to help you! :)