For Ripple Counter
for $2^n$ state no of Flipflop required is n. As this is async counter so Delay = $N*Propagation Delay$ so $4*10 ms = 40 ms$
For Sync Counter
Delay = $1*Propagation Delay$ as Sync counter has Clock same clock
Hence $Delay = 10ms$
Correct Ans is: $B$