okay so what you do here, mean is when you all all these numbers together and then divide them by the number of numbers here but because they want the difference between these two, you will take whatever you get after you added all them up then divided them by the total amount of number. then you take those two numbers and minus them and that will give you, your answer.
let me work it out for you
56+47+67+77+55+76+85+80+87+69+47+58
=804
divide that by the total numbers you have in the table that is, 12 numbers
so 804 divided by 12 gives you
=67
let me do the next one
52+32+65+63+52+70+72+61+54+43+29+32
=652
then you take that 652 and divide it by the total numbers given in the table which is also 12
so 652 divided by 12
=that’s 54,3
then you take the final answers
67-54,3
and your final answer is 12,7
hope this helped :)