Plz plz plz plz plz help me!!!!! Chemistry!!!!!! Right now!!?

This "4" comes from the fact that molarities are expressed "per 1000 cm3" and here you have a solution of "250 cm3". So, in order to calculate the equivalent moles in 1000 cm3 (molarity) you have to multiply by 4 (1000/250 = 4).