The volume of a cube is 729mm3. what is the height of the cube? How did you arrive at the answer

a cube has all equal sides

Volume of a cube  = S^3

729 = S^3

S = cube root (729)

S = 9

the height = 9 mm

Find total cost at both stores.

Fun Guys cost= 15 +5.5.a
where a is no of games rental

Game Bank Cost= 31 +3.5.a
where a is no of games rental

Since cost is equal in both
Therefore
31 + 3.5.a= 15 + 5.5.a
->2.a=16
->a=8
Therefore after 8 game rentals cost is same in both stores. 
cost= 31+ 3.5.(8)=59