In a survey 3/16 of the people said they preferred to visit self service restaurants. 5/8 said they would like to be served food by waiters. The remaining 75 said they have no clear preference. How many people preferred self-service?

Let $16x$  people take part in survey.

$\therefore$ The number of people who preferred self service

$=16x\times \frac{3}{16}=3x$

$\therefore$ The number of people who like to be served food by waiters

$=16x\times \frac{5}{8}=10x$

Remaining people = 75
 According to the question.
$\begin{array}{l}16x=3x+10x+75\\ \Rightarrow 16x=13x+75\\ \Rightarrow 3x=75\\ \Rightarrow x=25\end{array}$

$\therefore$ The number of people who preferred self service
$=3x=3\times 25=75$