Let's use an approach that may help you understand.
75% of what is 150. We can write this: 75/100 * what = 150. If you knew what "what" was you would know what to do, right? How is this solved? Well, we can divide both sides by 75/100. So we have: what=150÷75/100. OK. How do we divide by a fraction? We turn it upside down and multiply: what=150*100/75=2*100=200. So what is 200. In other other words, the number is 200. Now check: what is 75/100 of 200=75/100*200=75*2=150.
Now look at the answers we've been given. D fits: (75*2)/(100*2)=150/200=(part)/(whole). Whole is what we were looking for, and whole="what"=200.