Brittany's mom gave her $15.00 to buy school supplies. Brittany needs to buy 3 notebooks and some mechanical pencils.
If each notebook costs $2.99 and each mechanical pencil costs $1.50, how many mechanical pencils can Brittany buy using only the money her mom gave her?
The total cost of the notebooks is 3 notebooks * $2.99/notebook = $<<3*2.99=8.97>>8.97
The total amount Brittany has left after buying the notebooks is $15.00 - $8.97 = $<<15-8.97=6.03>>6.03
She can buy $6.03 / $1.50/pencil = <<6.03/1.5=4.02>>4 pencils. Answer: \boxed{4}.