To find the surface area of a sphere, you can use the formula:
\[ \text{Surface Area} = 4\pi r^2 \]
where \( r \) is the radius of the sphere.
Given that the diameter of the sphere is 40 inches, the radius \( r \) is half of the diameter:
\[ r = \frac{40}{2} = 20 \text{ inches} \]
Now, substitute the radius into the surface area formula:
\[ \text{Surface Area} = 4\pi (20)^2 \]
Calculating \( (20)^2 \):
\[ (20)^2 = 400 \]
Now substitute back into the surface area formula:
\[ \text{Surface Area} = 4\pi \times 400 = 1600\pi \]
Therefore, the surface area of the sphere is:
\[ \text{Surface Area} = 1600\pi \text{ in}^2 \]
So the final answer is:
\[ \text{Surface Area} = 1600\pi \text{ in}^2 \]