A rectangles perimeter is 30 inches and its length is 10 inches what is missing
The missing measurement is the width of the rectangle. In this case, the width can be calculated using the formula for the perimeter of a rectangle: P = 2L + 2W, where P is the perimeter, L is the length, and W is the width.
Given that the perimeter is 30 inches and the length is 10 inches:
30 = 2(10) + 2W
30 = 20 + 2W
2W = 30 - 20
2W = 10
W = 5
Therefore, the width of the rectangle is 5 inches.