we will write year in column B and column c respectively
2017 and 2018
then we will add months of year from January to December in the cells range from A2 to A13
then we will choose cell g5 and will write the diffrence formula
g5=cells with total attendance of 2018-cells with total attendance of 2017"
then finally we will use fill handle and drag the difference formula and copy the formula from g6:g12
look at attached file