Answer:
The length of the longer rope piece is 14 ft
Step-by-step explanation:
Let
x -----> the longer piece
y ----> the shorter piece
we know that
The sum of the longer piece plus the shorter piece must be equal to the length of the original piece
x+y=21
y=(21-x) -----> equation A
3x-7=5y ----> equation B
substitute equation A in equation B and solve for x
[tex]3x-7=5(21-x)\\3x-7=105-5x\\5x+3x=105+7\\8x=112\\x=14\ ft[/tex]
therefore
The length of the longer rope piece is 14 ft