If y varies directly with x, find the constant of variation with x = 4 and y = - 24

a: -6
b: 4
c: -96
d: 6

The price of a box of 15 cloud markers is $12.70. the price of a box of 42 cloud markers is $31.60. all prices are without tax, and the price of the packaging is the same for any size. how much would 50 cloud markers in a box cost? write an equation which will tell the price p for the number n markers in the box.