Given data:
- Size of the casting: 40x40x20 cm
- Radius of the cylindrical riser: 15 cm
- Height of the cylindrical riser: 20 cm

Volume of the casting:
The volume of the casting can be calculated by multiplying its dimensions:
Volume = Length x Width x Height
= 40 cm x 40 cm x 20 cm
= 32,000 cm³

Volume of the riser:
The volume of a cylinder can be calculated using the formula:
Volume of a cylinder = πr²h
where π is the mathematical constant pi (approximately 3.14), r is the radius, and h is the height.

Volume of the riser = π(15 cm)²(20 cm)
= 3.14 x 225 cm² x 20 cm
= 3.14 x 4500 cm³
= 14,130 cm³

Total volume:
The total volume of the casting and the riser can be found by adding their individual volumes:
Total volume = Volume of casting + Volume of riser
= 32,000 cm³ + 14,130 cm³
= 46,130 cm³

Time to fill the entire casting and riser:
To find the time required to fill the entire casting and riser, we need to consider the flow rate of the liquid metal.

Assuming a constant flow rate, the volume of metal poured per second can be calculated by dividing the total volume by the time taken:
Volume flow rate = Total volume / Time taken

Rearranging the formula, we can find the time taken:
Time taken = Total volume / Volume flow rate

The volume flow rate can be determined based on the size of the pouring basin and the pouring temperature, which are not given in the question. Therefore, we cannot calculate the exact time required to fill the entire casting and riser.

As a result, it seems that the given answer of '33.9' is either based on additional information not provided in the question or has been calculated using assumptions or approximations.

33.8