Which one of these expressions represent an area?

Question

I am confused about which expressions represent an area. a, b and c represent lengths

 

1. a(ab+bc)

2. a^2b

3. c(a+b)

4. 4(a+c)

Answer 1

For 1.  the final unit is length cubed (volume) - not possible area

For 2.  we don't know the magnitude of b; if b=2, - this is an area

For 3.  the final unit is length squared - possible area!!

For 4.  the final unit is length - not possible area

Let me know if this helps any.