ANSWER
24.1 cm
Step-by-step explanation
First, let us make a sketch of the question:
We see that the diagonal and the sides of the rectangle form two equal right angled triangles.
To find the length of diagonal, we have to apply Pythagoras Rule:
where hyp = hypotenuse = D
a and b = legs of the triangles (16 cm and 18 cm)
So, we have that:
The length of the diagonal is 24.1 cm.