Answer:
For the ratio between the price of the phones to be 9:11, the price of Emma's phone must decrease from $ 560 to $ 523.66. That is, the price of Emma's phone should decrease $ 36,364
Step-by-step explanation:
To answer this question, call x on Emma's phone and z on Sophie's phone.
We know that the price relationship between x and z is 7: 8
This means that:
We know that the price of Sophie's phone is $ 640
Entoces z = 640
Now we clear x

Then, if the new relationship is 9:11 then:

x = $523,636
For the ratio between the price of the phones to be 9:11, the price of Emma's phone must decrease from $ 560 to $ 523.66. That is, the price of Emma's phone should decrease $ 36,364