If the sample size is 53 and the population standard deviation is 12.87 then the standard error is ? (Answer to two decimal places)

If there are 36 observations then how many degrees of freedom are there for the t distribution (for a sample mean)?

If there are 50 observations in a sample, how many degrees of freedom are there? (The context here is for finding a t value when constructing a confidence interval or testing a hypothesis for the population mean).