Answer:
[tex]P=4x+10[/tex]
Step-by-step explanation:
Let
x -----> the length of Danielle's board in feet
y ----> the length of Tracy's board in feet
we know that
[tex]y=x+5[/tex] ----> equation A
The perimeter of the sandbox is equal to
[tex]P=2(x+y)[/tex] ----> equation B
substitute equation A in equation B
[tex]P=2(x+x+5)[/tex]
[tex]P=2(2x+5)[/tex]
[tex]P=4x+10[/tex]