3% of 400 is equal to 12. This can be calculated by dividing 3 by 100 and multiplying the answer with 400. Alternatively, you can also use the formula (Whole × Percent)/100 = Part, where the Whole is 400, the Percent is 3, and the Part is what we are calculating. Plugging these values into the formula gives us (400 × 3)/100 = 12.