Let us take the unknown number as b.
Sum of the number and 8 can be represented as,
8 + b
Therefore, five time the sum is,
5(8+b)
This is equal to 4, so,
5 (8 +b) = 4
This is the required equation.
The number is,
[tex]\begin{gathered} 5(8+b)=4 \\ 40+5b=4 \\ 5b=4-40 \\ 5b=-36 \\ b=-7.2 \end{gathered}[/tex]The number is, -7.2.