Answer:
width = 6 cm
Explanation:
since the diagonal is 15, and since both a rectangle has both sides, be double the diagonal.
15 x 2 = 30
diagonal (both sides) = 30
since we know the full perimeter and are looking to find the width, we will subtract both sides of the diagonal from the perimeter.
42 - 30 = 12
width (both sides) = 12
in order to get the width of one side, we will need to divide it in half.
12 / 2 = 6
width = 6 cm
hope this helps :)