4 P + 5 O2 ==> P4O10
If you have 24.98 grams of P and 74.99 grams of O2, how many moles of each compound do you have present?
Take the weight of each and divide them by their respective molecular weights.
e.g.
24.98 g of P *(1 mole of P/31.0g of P)= moles of P
I'll let you do the other one.