When order of mixed partial derivatives equal.

Pls , the question is in the picture!

Which ordered pair (c, d) is a solution to the given system of linear equations- c+2d=13 -9c-4d=-15

One of every 20 customers reports poor customer service on your company’s customer satisfaction survey. you have just created a new process that should cut the number of poor customer service complaints in half. what percentage of customers would you expect to report poor service after this process is implemented? 1.) 5% 2.) 10% 3.) 2% 4.) 2.5%