Hi I'm pretty new to Excel and have been hitting nothing but walls with this problem.

I need a way to increase one cell by 1, everytime a different cell increases by 3.

example; i need B10 to increase its number by 1, each time A10 increases by 3.

I have tried many formulas, but have only come close with; =COUNTIF(A10:A10,3)...

I need it to add 1, for every 3 points. (3,6,9 etc)

Any help will be greatly appreciated and thank you in advance!