Answer:
B
Explanation:
let's list everything out.
$35 for school supplies
$17.5 has already been used
$17.5 is left
pens only come in packs of 12
one pack of pens is $5
ok, so we know its definitely not C or D because they are less than 12
42 is not divisible by 12
since packs only come in 12's then it must be B.
good luck my friend!