Hello, I am needing help with a homework question.

The question is as follows:

A sample of 30 sales records from a convenience store has mean R140. It is known that the standard deviation of sales receipts in this store is R30. Use these values to test whether or not the mean sale value at the convenience store is different from R150, at the 5% level of significance. Test the hypothesis and establish the p-value. State your p-value correct to TWO decimal places.

My tutor has not explained this question to us very well

Thanks in advance