The original price was $17.92.

Calculate the first discount: $17.92*1/3=$5.97

The remaining amount after the first discount is: $17.92-$5.97=$11.95

Calculate the second discount: $11.95*0.145=$1.73

The remaining amount after the second discount is: $11.95-$1.73=$10.22

Calculate the third discount: $10.22*0.10=$1.02

The remaining amount after the third discount is: $10.22-$1.02=$9.20

**The price the nursery paid for the fertilizer was $9.20**

Calculate the price after markup, assuming the original selling price: $17.92*1.53=$27.42

Calculate the mark down: $27.42*0.42=$11.52

Calculate the price after mark down: $27.42-$11.52=$15.90

**a.The sale price was $15.90**

Calculate the new markup rate: ` ` ` 1-15.90/9.20=0.73 `

**b. The new markup rate was 73%**