A school department budgets $1,000 to purchase supplies. They must purchase a minimum of 50 items, consisting of calculators and protractors. Each calculator costs $15, and each protractor costs $5. Based on these constraints, the maximum number of calculators that can be purchased is .
If the department's budget increases by $100, and all other conditions remain the same, by how many will the maximum number of calculators that can be purchased increase?
5
10
15
20
