Slope, IF, Multiple Data Points

I'm trying to compute the slope of various products that have variable pricing ad quantity sources. The actual file is well over 5k rows and the product skus are in no particular order. I would like to input a slope formula with an IF statement that calculates the slope of only products that match that SKU.

I thought adding an IF statement into the array and saying IF the array within Column A has the item in Column A, select only that value.

{=SLOPE(IF($A$8:$A$20=$A8,$C$8:$C$20,),IF($A$8:$A$20=$A8,$B$8:$B$20,))}

I'm trying to calculate the information in the yellow Column of the attached file. I provided a check column and am seeing differences with my calculation.

Any help is greatly appreciated!