Answer :
Let x be the height, we know that the base is six times as long, this means that the base can be express as:
[tex]b=6x[/tex]Now, thas we know the height and the base we plug them in the equation for the area and solve for x:
[tex]\begin{gathered} 6x\cdot x=5040 \\ 6x^2=5040 \\ x^2=\frac{5040}{6} \\ x^2=840 \\ x=\sqrt{840} \\ x\approx28.98 \end{gathered}[/tex]Now, that we know the value of x we can calculate the length of the base (which is the longer side of the playground):
[tex]6(28.98)=173.88[/tex]Therefore, the length of the longer side is 173.88 ft