so d is correct as if u wanted to find out how much one thing cost u need to divide the number of the thing by its cost .An example is 20dollars for 4 apples. so 20/4=5 dollars for each apple.
This equation shows how much 3 erasers cost, which in this case its 4.41. the equation equals to 4/x as the cost of 1 eraser is the same. so if u wanted to solve this equation, u can use the cross method to multiply it so
3x=4.41*4
3x=17.64
x=5.88