Find the 4th term of the following problem

Question

(5x²-4)⁷

Answer 1

This is a problem to test your endurance, not your math skills!

(5x²-4)⁷ = sum from k=0 to k=7 of ₇C_k*(5x²)^k*(-4)^7-k.Of course, I don't know whether the 4th term is when k=3 or when k=4!

The thing with the C is the binomial coefficient and you just have to do a bunch of mindless algebra to get the right answer.