Multiple Criteria in IF function on Excel

[FONT=&quot]I need to put the below conditions in an excel formula. (preferred using the IF function)[/FONT]
[FONT=&quot]it's very tricky because the conditions vary depending on the units used, and inside each category, the price of the unit is different.[/FONT]
[FONT=&quot]category 1 * if you used, 0:50 units, the price will be 11 cents per unit.[/FONT]
[FONT=&quot]category 2 * if used 51:100, the price is 19 cents per the extra unit.[/FONT]
[FONT=&quot]category 3 * if used 0:200, the price is 21 cents per unit.[/FONT]
[FONT=&quot]category 4 * if used 201:350, the price is 42 cents per extra unit.[/FONT]
[FONT=&quot]category 5 * if used 351:650, the price is 55 cents per extra unit.[/FONT]
[FONT=&quot]category 6 * if used 651:1000, the price is 95 cents per extra unit.[/FONT]
[FONT=&quot]category 7 * if used 0:1001 or more, the price is 95 cents per unit.[/FONT]
[FONT=&quot]*Important*[/FONT]
[FONT=&quot]example to clarify,[/FONT]
[FONT=&quot]if one used 100 units, the the price will be (50*11) + (50*19) = 550 + 950 = 1500[/FONT]
[FONT=&quot]however if one used 101 units, the price will be 101*21 = 2121[/FONT]
[FONT=&quot]another example,[/FONT]
[FONT=&quot]if one used 700 units, the price will be (notice that we will check category 3 as a minimum price from 0) [/FONT]
[FONT=&quot](200*21) +(150*42) + (300*55) + (50*95) = 4200 + 6300 + 16500 + 4750 = 31750 cents = 317.5 Euros.[/FONT]
[FONT=&quot]notice that such variation takes place in category 1, 3 and 7.[/FONT]
[FONT=&quot]Thank you in advance.[/FONT]

First of all I want to ask you, is this a homework?
Second, you should set an example of the file with the expected results in multiple variants, it will be easier to understand the logic of the calculation.
Thirdly, how will you know when it is necessary to check categories 1,3,7. There must be a condition for this. Ie when?