An nth term in arithmetic sequence can be calculated using the following equation:
a(n) = a(1) + (n-1)d
Where a(n) = nth term, a(1) = first term, n= position of a(n), and d= common difference.
In the current task, a(1) = 1.6, n=100, d= 2.3-1.6=3.3-2.3 = 0.7
Therefore
a(100) = 1.6+(100-1)*0.7 = 70.9