This is a question based on Amdahl's law..Amdahl's law can be used wherever a section of a program uses some form of enhancement and other part remains unenhanced..
Speedup according to Amdahl's law is found as :
Speedup = 1 / [ 1 - f1 - f2 + .. +( f1 / S1) + ( f2/S2) + ( f3/S3) .. ]
where f1 , f2 etc. : fraction of enhancements
S1 , S2 etc : Speedup corresponding to each fraction of enhancement
So here f1 = 90% = 0.9
S1 = 30
Hence
Speedup = 1 / [ 1 - 0.9 + 0.9 / 30 ]
= 1 / [ 0.1 + 0.03 ]
= 7.69 [ Correct to 2 decimal places ]