The volume of a cylinder:
V = πr²H
A diameter is equal 2r (r-a radius), therefore 2r = 10in ⇒ r = 5in.
H = 3r ⇒ H = 3 · 5in = 15in
subitute:
V = π · 5² · 15 = π · 25 · 15 = 375π (in³) ≈ 375 · 3.14 = 1,177.5 (in³)
Answer: V = 1,177.5 in³