Asap charlie receives an email from his brother every 4th day and from his sister every 7th day. when will he receive an email from both on the same day?

Beth makes batches of bluberry muffins and banna muffins. each batchis 6 muffins. she makes 2.5 batches of bluberry muffins. how many batches of bananna muffins should beth make if she wants to have a total of 60 muffins?