The decimal fractions have no exact equivalent in hexadecimal or binary so I'll provide the same number of hexadecimal places as there are decimal places. That means there will be 4 times as many binary places as there are hexadecimal places.
a) Let's deal with the decimal fraction first. There are 4 decimal places so we'll get 4 hexadecimal places' accuracy. This means working out 164=6553610. We have to convert 0.251 so we need 65536×0.251=1645010 approx. This has to be converted to hex: 16450=4×4096+4×16+2=404216. The hex fraction is 0.4042. 757=2×256+15×16+5=2F516. So 757.2510=2F5.404216 approx. In binary this is:
1011110101.0100000001000010.
b) 0.510×163=208910 approx=8×256+2×16+9=82916. 0.510=0.82916. 1063=4×256+2×16+7=42716. So 1063.510=427.82916. Binary is 10000100111.100000101001.