Total amount $ 70.00
I need find the max amount of each level diff unit price first,
$ 1.00 x 10 unit= $10.00 -max amount 1
$1.50 x 10 unit =$15.00 -max amount 2
next i need to check is it my total amount is more than the max amount 1 or 2 or less than max amount 1 on above .
in this case it $70.00 which is amount have exceeding both of max amount
1st step
First 10 unit of $1.00/unit price=$10.00
Total amount -Max amount of First 10 unit=Balance 1
$70.00-$10.00=$60.00
2nd Step
Second 10 unit of $1.50/unit price=$15.00
Balance 1-Max amount of Second 10 unit=Balance 2
$60.00-$15.00= $45
3rd Step
finally i have last unit price $2.00 for the remaining Total amount, that mean my Balance 2 divide by $2.00/unit Price i will get total usage for $2.00/unit Price
Balance 2 / $2.00
$45.00/$2.00= 22.5 unit usage
Finally result : Total unit Usage
1st step Unit Usage + 2nd step unit usage + 3rd step usage
=10 unit + 10 unit + 22.5 unit
Grand total = 42.5 unit
