1 Which gives us an answer of 0.010869565cm3.  The final step is to convert your volume into ml. As 1cm3 = 1ml it's a 1:1 conversion. So, we don't need to do anything and therefore have our answer. 10mg of sunflower oil is 0.010869565 ml.
No. When a child reaches age 8 (regardless of weight) OR reaches 80 pounds (regardless of age), a properly fitted seat belt may be used instead of a child restraint/booster to restrain the child. However, keep in mind that the seatbelt may not fit properly even if the child is 8 years old or weighs 80 pounds. The law does require that children stay in a child restraint or booster seat until the seat belt fits properly on its own.
If you can safely keep your child in a harnessed car seat for a while longer, do it. Most 3-year-olds are not ready to ride in a booster seat in the car, even if they fit within the manufacturer's height and weight guidelines. Best practice is to keep your child in a harnessed car seat to at least 40 pounds and 4 years, but preferably longer. Many convertible car seats have harnesses rated to 65 or even 90 pounds. Most children can fit into the harness of one of these car seats well past age 4.