ANSWER
[tex]19.5\%[/tex]EXPLANATION
To find what percentage 78 is out of 400, we have to divide 78 by 400 and multiply by 100.
That is:
[tex]\frac{78}{400}\cdot100[/tex]Simplify:
[tex]\begin{gathered} \frac{78}{400}\cdot100 \\ \Rightarrow19.5\% \end{gathered}[/tex]That is the answer.