To represent $f(t)$ using a combination of Heaviside step functions based on the given graph, we need to break down the function's behavior at each point where it changes.

Step 1: Identify Key Points and Values

1. Initial Value: From $t = 0$, the function $f(t)$ appears to be at $0$.
2. At $t = 1$: $f(t)$ jumps to $2$, indicating a step at $t = 1$.
3. At $t = 2$: $f(t)$ increases to $4$, showing a linear rise from $2$ to $4$.
4. At $t = 3$: $f(t)$ becomes constant at $4$ until it drops back to $0$ at $t = 4$.

Step 2: Define $f(t)$ in Terms of Heaviside Functions

Let $h(t - c)$ represent the Heaviside function, which is $0$ when $t < c$ and $1$ when $t \ge c$.

Using this notation, we can write $f(t)$ as follows:

1. From $t = 0$ to $t = 1$, $f(t) = 0$.
2. At $t = 1$, there is a jump to $2$, which can be represented by $2 \cdot h(t - 1)$.
3. From $t = 1$ to $t = 2$, the function increases linearly, which can be represented by $2(t - 1) h(t - 1) - 2(t - 2) h(t - 2)$.
4. At $t = 3$, it remains at (