How do I derive sec^7*x^3

I have the answer

21x˛sec^6*x^3(secx^3*tanx^3)

but i'm not sure how it comes about. I've tried to treat it using the chain rule and product but neither seems to work. I'm really confused about how to derive something where the trig function has an exponent like cos˛x.

And I know i've been asking a lot of questions, i'm really trying to improve in calc so sorry for the barrage of easy questions and thanks a bunch. I can't explain how much of a help you guys have been