The rate of change = change in profit/change in dolls sold
Let us use the values in the first two columns to get our slope.
When amount of doll sold S1 = 1, profit P1 = $3
When amount of doll sold S2 = 2, profit P2 = $6
Rate of change = P2-P1/S2-S1
Rate of change = $6-$3/2-1
Rate of change = 3/1
Rate of change = 3
Hence the rate of change (slope) is 3
Note that no matter the two columns you decide to use, you will still get the same value for your slope whcih is 3