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12a)  4L - 6 = Perimeter

13) 4(6x + 9)

Step-by-step explanation:

for #12:  two sides of the rectangle are referred to as L

The other two sides can be referred to as L-3 (these sides are the width, which are 3 less than the length)

Perimeter = sum of all sides; so, 2L + 2(L-3)

P = 2L + 2L - 6

  = 4L - 6

12. The expression is 2L+2(L-3)

13. The answer is 6x+9

Step-by-step explanation:

12. The perimeter of a rectangle is 2*length +2*width. So, in this case (when L is the length of the rectangle) the perimeter should be 2L+2(L-3). If you simplify you will get 4L-6.

13. The perimeter is just the value you get when all the sides of a shape are added. A square has 4 equal sides. So, just divide the perimeter, which in this case is (24x+36), by 4. You should get 6x+9.