The perimeter of a rectangle is given by p=21+2w.fine it's area when it's length (I) is 15cm and its width (w) is 8cm.?

Given:
Perimeter (p) = 21 + 2w
Length (l) = 15 cm
Width (w) = 8 cm

We know that the perimeter of a rectangle is given by the formula:
Perimeter = 2(length + width)

Substitute the given values into the formula:
21 + 2w = 2(15 + 8)
21 + 2w = 2(23)
21 + 2w = 46
2w = 46 - 21
2w = 25
w = 25/2
w = 12.5 cm

Now, we can calculate the area of the rectangle using the formula:
Area = length x width
Area = 15 cm x 12.5 cm
Area = 187.5 cm²

Therefore, the area of the rectangle is 187.5 cm².

The given formula for the perimeter of a rectangle is incorrect. The correct formula for the perimeter of a rectangle is P = 2(l + w), where P is the perimeter, l is the length, and w is the width.

Using the corrected formula, we can find the perimeter of the rectangle with a length of 15 cm and a width of 8 cm as follows:

```
P = 2(l + w)
P = 2(15 cm + 8 cm)
P = 2(23 cm)
P = 46 cm
```

Therefore, the perimeter of the rectangle is 46 cm.

We can find the area of the rectangle by multiplying its length and width. Using the given values, we get:

```
Area = l - w
Area = 15 cm - 8 cm
Area = 120 cm²
```

Therefore, the area of the rectangle is 120 square centimeters.