Sketch the graph of the function $$k(t) = \int_0^t \left( \delta(w-1) -\delta(w-4) \right) dw, \quad 0\leq t < \infty.$$ Use the graph to express $k(t)$ in terms of shifts of the Heaviside step function $h(t)$.

$\displaystyle k(t) =$