Can you please show all steps and if you use R studio please give me the function as well

Suppose we have a set of n values: {961, 962: I 96111: 3'11} The sample mean of the above set is f. Prove that if we multiply every value by k, then the new average will be: New average = k9? (Hint: Use the formula for the sample mean with the \"new\" set plugged in, then simplify.)