Question 1164094
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The perimeter is 30, so the semi-perimeter (length plus width) is 15.<br>
Since the length is 3 more than the width, simple mental arithmetic gives us 9 and 6 as the length and width.<br>
The area is length times width; the length of the diagonal is the length of the hypotenuse of a right triangle with legs 6 and 9.<br>
You can do the calculations....<br>