The area is one side times the other side
Make the other side x.
12x=42
x=42/12=3.5
The perimeter is 2x+2y where x and y are sides of the rectangle.
P= 2(3.5)+2(12)=7+24=31 inches
Hope this helps.
Answer:

Step-by-step explanation:
We first translate the statement into an equation:

Then we simplify:

Well I don't know if you are looking for the variable but here it is :)