I've been trying to crack open a calculus book so I can get a head start when I take calc with analytical geometry 1 next semester but one of the first problems is stumping me. I think I'm an idiot. Should I just kill myself?

The problem is:
find the slope of the tangent line to the graph of F at the point p(a,f(a))

with F(x) = 5x/\2 - 4x

It's the chapter on limits. The first section.
I keep trying different things like F(a)/a to find the slope but they don't work. The book says the solution should be 10a - 4 but I don't get how.