Since the shape is not given, it's not easy to determine the actual perimeter. Regardless, it's important to keep in mind that the perimeter and area are independent of each other.
That said, assuming that this is a rectangle (since this amount of information is insufficient for any other 2D shape I can think of), it would simply be 2(12.4)+2(5.9), or 24.8+11.8, or 36.6.
Saying actual perimeter typically means just that: the ACTUAL perimeter of a specified shape, which is why it's odd that this problem does not include a shape.
The perimeter efficiency, for example, compares the actual perimeter of a shape with the circumference of the circle that would be required to enclose the same area. Since a circle will enclose any given area with the least amount of perimeter, it is said to be 100% efficient as an area enclosure.