A Sample of 18 widgets has a mean of 47. And standard deviation of 99.550, At 99

A Sample of 18 widgets has a mean of 47. And standard deviation of 99.550, At 99% confidence, the upper limit with 3 decimal places
the solution to that is:
upper limit =47 + 2.898*99.550/sqrt(18) =114.999
How did the 1.833 came about when I check the Zscore of a 99% confidence it would be (1-.99) = .01/2 = .005 Zscore of ..005 would be 3.355