If an object moves along a line so that it is at y=f(x) = 4x² - 3x at time x (in seconds), find the instantaneous velocity function v = f'(x), and find the velocity at times x = 1, 3, and 5 seconds (y is measured in feet).
A) v = f'(x) = ___ ft/sec
B) v = f'(1) = ___ ft/sec
C) v = f(3) = ___ ft/sec
D) v = f'(5) = ___ ft/sec