Answer is A
42 can be represented as 1*32+0*16+1*8+0*4+1*2+0*1 = 42, so the binaray representation is (101010)2.
And fraction part can be obtained as $\frac{1}{2}+\frac{1}{4} = 0.75$, the binary representation is .110
So, the total binary representation of 42.75 is (101010.110)2