#1 There is no area of a cube. There is only a volume.
#2 The formula is

where s is the side.
Substitute 729 in V since that is the volume.

Take the cube root and you will get
9.
So the formula is
and the side is 9.
Given:
Cost of small candles = $4.00
Cost of large candles = $6.00
They have at most 50 candles, and want to make at least $100.
To find:
The system of linear inequalities represents the situation.
Solution:
Let x be the number of small candles and y be the number of large candles.
At most 50 candles means total candles must be less than or equal to 50.

Want to make at least $100. It means, the total sales must be greater than or equal to $100.

Therefore, the inequalities in the system of linear inequalities are
and
.
39/40 as a decimal is 0.975
Can you make the picture a little clearer