Calculate the derivatives of the following functions at the specified values of the independent variable:

(a) y = 16x² at x = x1,

(b) y = 16x² at x = 4.

(c) y = bx² at x = 4.

(d) s = 16t² at t = 5.

(e) A = πr² at t = 5.

(f) s = 2.6t² at t = 5.

(g) y = −2x² at x = 4.

(h) y = 1/2x² at x = x1.