8 four bit CLA are needed to create a 32 bit Adder
P & G Generator will take 1 gate delay (as EXOR and AND will operate in parallel)
Carry generator will take 2 Gate delays (All AND in parallel (1)+All ORs in Parallel(1)=2)
C4 will be available to next CLA and next CLA will Take 2 gate delays also . During same time Sum Generator of first will calculate sums not taking any extra time
same thing will happen for all 8 carry generators 2*8=16 .During the same time 7 Sum generators will calculate sum without taking extra time as all are working in parallel
Sum generator of last CLA will take 1 gate delay (all EX-or in parallel)
total 1+2*8+1=18
Answer option B