We are given the following information
Carlos works a total of 86 hours in four weeks.
He works 18.5 hours each week for three weeks.
To determine how many hours Carlos work in the fourth week, we can set up the equation
[tex]86=18.5(3)+x[/tex]We can make x the subject of the formula
[tex]\begin{gathered} x=86-18.5(3) \\ x=86-55.5 \end{gathered}[/tex]Simplifying further
[tex]x=30.5[/tex]Therefore in the fourth week, Carlos will work 30.5 hours