Explanation:
The total number of customers in 2 weeks is 300+360=660
=> week 1, % client's: 360/660 × 100% = 54,54%
Week 2, % client is : 100% - 54,54% = 45,56%
% Change customer of the week 1 compared with week 2 is: 54,54% - 45,56% = 9,08%
(I'm from a country where I don't speak English, so there's nothing wrong with looking forward to your help)