Here we need to find the CPI of each instruction in pipelined system..
So we know :
CPIpipeline = CPIideal pipeline + No of stalls / instruction
Now here stall is due to branch instruction...
So branch penalty = Stage at which target address is found - 1
= 4 - 1
= 3
Fraction of branch instruction = 0.4
Hence CPI = 1 (CPI of ideal pipeline) + 0.4 * 3
= 2.2
Hence time taken by 1 instruction = CPI * Cycle time
= CPI / Clock frequency
= 2.2 / ( 2.3 * 109 ) s
So no of instructions / sec = (2.3 * 109) / 2.2
no of million ins / sec = (2.3 * 1000) / 2.2
= 1045.46 MIPS
NOTE : wrong calculation by madeeasy