How many 6 digit combinations are there using only numbers 1-9?

Idon’t understand this.. will someone ? will mark brainliest along with 20 points.

Round each of the decimals to the nearest hundredth a. 0.596 b. 4.245 c. 53.6843 d. 17.999

The roof of a farm silo is the shape of a hemisphere and is made of sheet tin. if the diameter of the silo is 126.5 feet, how much sheet tin is needed to make the roof? (use π = 3.1416.)