Since Walter split the trip into 3 sections of equal time, we can divide the total miles in three to get the following:
[tex]\frac{1404}{3}=468[/tex]Then Walter drove 468 miles in each section. Now, he drove at an average speed of 52 miles per hour, then:
[tex]\begin{gathered} 52mi\rightarrow1h \\ 468mi\rightarrow x \\ \Rightarrow x=\frac{468mi\cdot1h}{52mi}=9h \\ x=9h \end{gathered}[/tex]therefore, Walter drove for 9 hours in each section.