A-level stats question

Hey guy's i'm stuck on this question,i've got Ho: u = 0.034 ND h1: U /=0.034 and N(0.034, 0,000409/50) but not sure what to do from here and help or guidance will be appreciated the question is as follows:

The level, in grams per millilitre, of a pollutant at different locations in a certain river is denoted by
the random variable X, where X has the distribution N(n, 0.0000409).
In the past the value of n has been 0.0340.
This year the mean level of the pollutant at 50 randomly chosen locations was found to be 0.0325
grams per millilitre.
Test, at the 5% significance level, whether the mean level of pollutant has changed