EMERGENCY! Please give me the correct answer!

If x varies directly as y, and x = 7.5 when y = 10, find x when y = 4

What will be the end result for the taxpayer who filed his federal income tax return using the 1040ez form shown belowa he'll owe $173b he'll receive a refund of $173c he'll owe $3921d he'll receive a refund of $3921

Based on the diagram above, a student determined the hypotanuse of the triangle to be 6√3. determine if the students answer is correct. if not correct find the correct length