First we calculate the test statistic, which we do using a t-table because we don’t know the population standard deviation. This table needs the number of degrees of freedom, n-1=34.
T=(1860-µ)/(102/√35) where µ is the population mean. Look up T for 34 dof and a 2-tail test at a confidence level of 99% (significance level 100-99=1% or 0.01). T=2.73 approx. So µ is defined by a range, T=±2.73, and µ=1860±2.73(102/√35)=1860±47, so 1813<µ<1907.