let
x------> pieces number one
y------> pieces number two
we know that
x+y=70 ft------> x=70-y------> equation 1
x+10=3y--------> equation 2
substitute equation 1 in equation 2
[70-y]+10=3y--------> 70-y+10=3y----> 4y=80----> y=20 ft
x=70-y----> x=70-20----> x=50 ft
the answer is
50 ft and 20 ft
