In 2013 , the estimated world population was 7.1 billion. Use a doubling time of 66 years to predict the population in 2026, 2054, and 2111. What will the population be in $2026 ?$ The population will be $\square$ billion. (Round to one decimal place as needed.)

Step 1 ：The question is asking for the estimated world population in 2026, given that the population was 7.1 billion in 2013 and that the population doubles every 66 years.

Step 2 ：To solve this, we can use the formula for exponential growth, which is: \(P = P0 \times (2)^{t/T}\) where: \(P\) is the final population, \(P0\) is the initial population, \(t\) is the time elapsed, and \(T\) is the doubling time.

Step 3 ：In this case, \(P0\) is 7.1 billion, \(t\) is 2026 - 2013 = 13 years, and \(T\) is 66 years.

Step 4 ：We can plug these values into the formula to find the estimated population in 2026.

Step 5 ：Let's calculate this: \(P0 = 7.1\), \(t = 13\), \(T = 66\), \(P = P0 \times (2)^{t/T} = 8.138645569020689\)

Step 6 ：The estimated world population in 2026 is approximately 8.14 billion.

Step 7 ：Final Answer: The population will be \(\boxed{8.1}\) billion.