Insane trivia

So at Caribou shops, we offer a trivia question everyday. Guests that get it right get $0.10 off. Normally the question is "Who was the 10th president?" or something like that. Check out today's. I've copied and pasted the e-mail below:

Email:

At the Grand and Snelling store this morning, the trivia question was as follows:

Calculate the simple derivative of the following function:

f = 2x squared + 2xy squared

Assume y is a constant


I have a few thoughts:
I think we've taken the reduction in LSM discounting too far. That is a VERY difficult trivia question
Can someone check the number of trivia discounts given out at this store today? Anything higher than $2 and I suspect fraud
Can someone answer the question for me? I thought I knew how to do it, but I was wrong. It made me feel old, and like I may have invested thousands of dollars in useless math education.

Thanks!
Matt