So you have a base of 48 m (8*6) multiply that by the height(1/10m) you would get estimate 4.8 meters cubed. Since she has 5 meters cubed she will indeed have enough.
Find a common denominator of the two. Change the fraction 1/2 to 2/4. Now you add 3 and 2 and 2/4 and 3/4. You will get 5 and 5/4 which simplifies to 6 and 1/4. This means you will need more than one bag
Your answer is going to be 21 u just subract from the number to get ur answer
I would do 10x10-8x8 which is 36 which is 6 times it self
So A=6 in.