Suppose t=1ns, there are total 100 operations, 80 fixed point operations and 20 floating point operations,
Time taken by design D = 80*1ns + 20*2ns = 80+40 =$120 ns$
Time taken by design D1 = 1.3*80 + 0.7*40 = 104 + 28 = $132 ns$
Time taken by design D2 = 0.6*80 + 1.1*40 = 48 + 44 = $92 ns$
Now, we can see that D2 is fastest, D is faster than D1.
Hence (B) is correct option D2 > D > D1