help my friend, it's 3am for me

[native stream]

Draw the f'(x) first. If the generic nature distracts you, imagine a parabola for it. If that still feels too generic, imagine a quadratic function f'(x) = ax^2 + bx + c and make it fit with the constraints (or directly f'(x) = -a(x-2)(x-4), if that feels more intuitive for your brain), draw that and then this gives a sense of how the slope of f moves.