For 100 instructions,

first 40 instructions are taking 3 cycles in PO phase. So first instruction will compete after 7 clock cycles and second instruction will complete after 10 clock cycles and so on...It is like an AP

7,10,13,...... up to 40th terms

So last term = 7 + 39 *3 = 124

first 40 instructions will be complete after 124 clock cycles.

For next 35 Instructions

41st instruction will complete after 126th clock cycle and 42nd instruction will complete after 128th clock cycle and so on...

126,128,.....up to 35th terms

So last term = 126 + 34*2 = 194

Next 35 instructions will be complete after 194 clock cycles.

For the remaining 25 instructions,

76th instruction will be complete after 195th clock cycle and 77th instruction will be complete after 196th clock cycle and so on...

195,196, 197, .....up to 25 term

So last term = 195 + 24 *1 = 219

hence, overall 100th instruction will be complete after 219 clock cycles...

**Another way:**

There are 100 Instructions out of which first instruction will take complete time, I mean (1 cycle for IF, 1 cycle for ID,1 cycle for OF, 3 cycles for PO and 1 cycle for WB) , So first instruction will take 7 clock cycles and remaining instructions will depend upon how much each individual instruction spending time in PO stage. Hence time would be:

7 cycles(for First instruction) + (40-1) * 3 + 35 *2 + 25*1 = 219 clock cycles..