Answer:
,

Explanation:
The diagonal splits the rectangle into two right triangles so we can use Pythagorean theorem to find the length of the missing side.
Pythagorean theorem states that a^2 + b^2 = c^2 where c is the hypotenuse and a and b are the other two sides
So we can label our unknown side as x
x^2 + 9^2 = 18^2
x^2 + 81 = 324
Subtract 81 from both sides to isolate the x
x^2 = 243
Find the square root of both sides
√x^2 = √243
x ≈ 15.6
(The instruction said round to the nearest 10th).
So now we know
l = 15.6m and w = 9m
P= 2l + 2w
A= lw
P= 2(15.6) + 2(9)
P= 31.2 + 18
P= 49.2m
A=15.6(9)
A=140.4m^2