Is it not supposed to be 12/4 +1

In the original problem, the total equivalent resistance of the parallel combination was $4 \text{ } \Omega$. The voltage across this combination (and thus the total voltage supplied by the source) was $12 \text{ V}$.

According to Ohm's Law, the total current ($I$) is calculated as:

$$I = \frac{\text{Total Voltage}}{\text{Total Equivalent Resistance}}$$ $$I = \frac{12 \text{ V}}{4 \text{ } \Omega}$$ $$I = 3 \text{ A}$$

Adding $+1$ to the denominator or the result would imply an additional $1 \text{ } \Omega$ resistor in series with the parallel combination, or some other component not present in the original circuit diagram. Based on the image you provided, there was no such additional resistor.