Suppоse nоw thаt the per unit price оf tаcos decreаses from $6 to $2 and that the income level and the per unit price of nachos remained unchanged at $48 and $3, respectively. The decrease in price of tacos increases Alya's quantity demanded of tacos by _______ units. This increase in the quantity demanded of tacos comes from a substitution effect approximately equal to ______ units, and from an income effect approximately equal to _____ units. (Fill in the blanks.)