Gilberto needs to purchase baseballs and bats for his youth baseball league. He'll need at least 15 pieces of equipment, but he only has $435 to spend. Baseballs cost $20 each and bats cost $35 each. Which is a combination of baseballs and bats that Gilberto can afford to buy?
a.) 9 baseballs and 7 bats
b.) 10 baseballs and 7 bats
c.) 8 baseballs and 6 bats
d.) 8 baseballs and 10 bats