Determine an equation of the tangent line to y=(x^4)(e^-x) at the point (4, 256/e^4), then solve it for y.?

This is a calculus problem and no matter how many times of trying to solve this using basic calculus knowledge, I can't seem to figure it out. I don't know if it's because I keep overlooking little typos I may have made, or if there are important steps I missing. Please help!!