The number 6 could replace the gap :)
Answer: 6
Step-by-step explanation:
7 - 3 = 4
3 - 4 = 0
0 - 6 = -6
Your calculator probably only evaluates in base 10 (ln is base e but we won't use that today)
so

where c is the new base
so if you wanted in base 10

using calculator, that is about 2.16096
Answer:
Diameter is basically double the radius, a physical representation of it is a full line that goes across the middle of the circle, if that makes sense. So you do 2 x 2 = 4 units
Hope that answers your question