Question

16 POINTS!! The solid in the diagram has a surface area of 18 units2. If a cube is added on the green face, what will the new surface area be? A) 20 units2 B) 21 units2 C) 22 units2 D) 23 units2

Answer 1

the complete question in the attached figure

Let 
x------> length side of a cube

we have that
[surface area original]=18 units²

surface area original=x²*[number of faces]
number of faces=2*[4+4+1]-----> 18 faces

surface area original=x²*[18]
18=18*x²-------> x²=18/18---------> x=1 unit

If a cube is added on the green face,the new surface area will be
18+4*[area of one faces]-----> 18+4*1²----> 22 units²

the answer is
22 units²