Clear output box when input Dropdown Box's are changed!!!!!

I got all three dropdowns to be dependent on each other, now however, whenever I change the value in the top Input Dependent Box M39, I would like M43 & M47 to appear blank. I want these two cells to appear blank until you select the dropdown which will allow you to select your values of choice. I am thinking I could use an IF statement or a macro but I don't really know how I would go about doing this. If you could help it would be greatly appreciated! I have been trying to look up how to do this for a while!

Thanks beforehand,