Answer:
31cm
Step-by-step explanation:
First, we need to set up the equations
perimeter is equal to 2 times the width plus 2 times the length
p=2w+2l
86=2w+2l
then you set up what the length is
length is equal to 2 times the width plus 7
l=2w+7
then use substitution to find the width
86=2w+2(2w+7)
86=6w+14
72=6w
12=w
then you take the width and plug it into the length
l=2(12)+7
l=31
thus the length is 31cm
