Answer:
126 cm^3
Step-by-step explanation:
Use volume formula (Bh=V): 21×6=126
You may go the super easy way and choose 1 as the whole number and 0.28 as the decimal number. Then you'd obviously have 
Otherwise, to be a bit more creative, you can observe that

And since 1/25=0.04, you can also choose 7 as the integer, and 0.04 as the decimal to get

This is the well known Monty Hall problem.
You have more chances of winning by switching doors.Let A,B,C denote the events "The ferrari is behind A" and so on
Let HA,HB,HC denote the events "The host opens A" and so on
By Baye's formula,

whereas

!!
I think it is 18 Hope this helps. :)