I need a picture so i can help you out.
Well perimeter is lengthx2 and widthx2 so 7x2=14
then 64-14=50
50÷2= 25
length=25
Answer:
multiply the factor 2 with each term inside the parentheses
I'll use my own formula (similar to yours tho)

A=future amount
p=invested
r=rate in decimal
n=number of times per year compounded
t=time in years
so
when will A=2P
subsitute 2P for A
also quarterly means 4 times a year or n=4
and 12%=0.12=r
so

divide both sides by P

simplify


take the ln of both sides



divide both sides by 4ln(1.03)

use calculator
5.86244=t
about 5.9 years
It will either be 0.28 or 0,42 depending of what 12-8 means