It will be understood that population 6,000 billion (6*10^12) in 2017.
If this is not the case, follow the logic and the final number can be adjusted easily.
Mathematical answer:
In 2017: 6,000 billion=6000*10^9 =6*10^12
rate of increase = 1.3% per year (assumed constant)
final year = 2100
Population estimate in 2100
=6*10^12*(1.013^(2100-2017))
=6*10^12*(1.013^(83)
=6*10^12*(2.921352509198383)
=17.528*10^12
=17,528 billion.
