get number of item from slot

hello! I've made an I.E.D.  and i have problem with my procedure, everything work fine except for this part https://ibb.co/gVSTs3g at the very end where i want to make the explosion bigger if we put more death powder.... it doesn't work instead it just do a tiny explosion that doesn't even destroy the item from how weak it is. https://ibb.co/rbD6x1Y ( here how my gui look ). i can take any kind of advice