Calculating material needed for a lamp shade with an allowance for the seam.

Question

I wanted to solve this problem but my English is bad and not familar with tailor stuff....

A lamp shade is in the form of a frustum of a cone with slant height 7 inches, radii of bases 3 inches and 7 inches respectively. How much material is used in its construction if 0.75 inches is allowed for the seam?

I wanted to solve the problem but I do not know what is a seam is.

Can somebody just give me a drawing for it so I can solve it.

Thanks!

The answer should be: 221.66 square inches

This question is from the book: Solid Mensuration, Second Edition by Willis Kern and James Bland

Answer 1

Slant length $L= 7", R= 7", r=3" $, with overlap assumed seam width $S= 0.25"$ gives (near to what the answer should be).

$$ \pi L (R+r)+ L ~S= 221.661" $$ With $S= 0.75"$ the area is more, consider for discarding.