Explanation:
remember, the volume of a cylinder is
ground area × height = pi×r² × height
with r being the radius of the ground (or top) circle, which is half of the diameter.
I am not sure, how your teacher wants you to do estimates.
for me that means rounding the base numbers to "good" numbers (typically whole numbers or other numbers we can easily then calculate in our heads).
so, I would say, the diameter is about 3 in, that means the radius is 3/2 in.
the height is about 4 in.
that means my estimated volume is
pi × (3/2)² × 4 = pi × 9/4 × 4 = 9pi
if I round pi (3.1415...) to 3, then my full estimate would be
9×3 = 27 in³
but, just in case, pi is often "emulated" by 22/7 for estimation.
we would then have
9×22/7 = 198/7 = 28 2/7 = 28.28571429... ≈ 28 in³
I don't think this is in any of its forms considered an easy and nice estimation anymore.
again, it depends on what your teacher wants you to do when saying "estimate". as you can see, there is a whole in³ difference.