Ok , the first and second addres is right but how he is calculated the 100th address? The 100th address should be (ending range) 7+(8x99) then converting into binary, grouping 8 binaries and make octed ,

How he calculated 100th its wrong, The 100th address should be below if you increment step by step:

120.60.3.24 - 120.60.3.31

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If 120.60.3.24 - 120.60.3.31 is wrong then please explain step by step for calculation nth address

An ISP is granted a block of addresses starting with 120.60.4.0/22. The ISP wants to distribute these blocks to 100 organizations with each organization receiving just eight addresses. Design the subblocks and give the slash notation for each subblock. Find out how many addresses are still available after these allocations