Question

if the edge of a cube is tripled find the ratio of surface areas

Answer 1

Let the edge of the cube. 
Then the surface area is 6L² 
If the edge is doubled, the L becomes 2L 
Hence the surface area then becomes 6(2L)² = 24L² 
So the surface area becomes 4 times larger. 

So by the same way, the surface area becomes 9 times larger when the edge is tripled.