Suppose, i have 3 incentive slabs

No.of sale incentive slab

1-10 no.of sale*8
11-20 no.of sale*10
21 and above no. of sale*15

What formula i have to insert in the incentive column , so i will get the
incentive of every salesman if i fill only the no. of sale in the column left
to incentive slab column ?If this works i will be able to save a lot of time
and energy so please help and explain in details with examples.
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With Thanks
Regards

Rajesh Chandra