The variables [[$ a $]], [[$ b $]] and [[$ c $]] are lengths in meters. Use unit examination to examine whether the following formulas calculate length, area, or volume.

a) [[$ 2a + 2b + c $]]

Answer: The formula is used to calculate .

b) [[$ 4a^2 + 3b(a + c) $]]

Answer: The formula is used to calculate .

c) [[$ 3a^2c + 2abc $]]

Answer: The formula is used to calculate .

d) [[$ a + 2ab + c^3 $]]

Answer: The formula is used to calculate .