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For how answer my question this will be the last question can you answer in math subject

In a class, there are 12 girls. if the ratio of boys to girls is 5: 4 how many boys are there in the class

Ateacher wanted to buy a chair, a bookshelf, two tables and a desk. she spent $900 for all five items and the chair and the desk combined 70% of her total. if the bookshelf cost $50, how much did each of the tables cost?