Find the value of the missing variable

21. y varies directly with x. If y = -4 when x = 2, find the constant of variation.

22. y varies inversely with x. If y = 40 when x = 16, find k.

23. y varies inversely with x. If y = 7 when x = -4, find y when x = 14.

24. y varies directly with x. If y = 105 when x = -5, find y when x = 1.6.

25. y varies directly with x. If y = 75 when x =25, find x when y = 25. (Round off to the nearest hundredths)

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