What is the number of moles Phosphorous (P) in 5.00 g in the 15-30-15 fertilizer

15 - 30 - 15 indicates the percentages of Nitrogen - Phosphorus - Potassium respectively. Thus, the fertilizer has 30% Phosphorus (by mass)

Mass of phosphorous = 5 * 0.3

= 1.5 grams

Atomic mass of Phosphorous:

31

moles = mass / Ar

moles = 1.5 / 31

moles = 0.048 mol