13.99 kilometers is the diameter.
Divide the circumference (43.96) by 2(pi), which should give you a radius of 6.99. You should then proceed to multiplying that by 2, since radius is half of the diameter, giving you 13.99.
This can be answered in many different ways, assuming this is a short answer response. Overall, you should have these points:
1. It culturally united [North Africa]
2. It spread new trade routes and therefore increasing the economy.
3. Made the mysterious continent much more known to outsiders.
Additionally, you should give examples of how this can be seen. In other words, prove with historical context that this is what Islam did.
