It is just asking how many meters tall are doors usually at. Clearly 30 meters isn't reasonable so just say how tall most doors are in meters.
Answer:
2 is a number and "twice a number" means multiply by 2.
Original price:
6(3.5)
21
New Price:
1.15(21)
24.15
24.15-21
$3.15 more
the answer to your question is 4^6
