Answer:
$8.50
Step-by-step explanation:
I don't know what Alls are, but if Carlos insists, we can calculate how much he can spend on Alls with the expression:
($31.50) + r $40
This says the sum of what Carlos has already spent (hot dogs and hamburgers) plus the amount he spends on Alls (rolls?), r, must be equal to or less than the $40 he has allowed himself to spend.
($31.50) + r $40
r $40 - $31.50
r $8.50