Quickly! (will give brainliest if answer is correct!

First you want to find the area of each side.
 
For side 1: 4 x 3 = 12cm^2
Multiply it by 4 because its a cube: 12 x 4 = 48cm^2
(Side 2 is included with side 1)
 
For side 3: 4 x 4 = 16cm^2
Multiply it by 2: 16 x 2 = 32cm^2 

Add both of these together to get the final answer of 80cm^2

6x + 12 = 32
6x = 32 - 12
6x =20
x = 20/6
x = 10/3