So we're using Left Hand Sums.

First find the height of each cylinder.

It's six subintervals, so we'll have six cylinders.

Note that the height function is the upper half of the circle of radius 3:

The radii for the six cylinders are the y-values of the left end points:

[0, 1/2]

[1/2, 2/2]

[2/2, 3/2]

[3/2, 4/2]

[4/2, 5/2]

[5/2, 6/2]

The Volume formula is

for example:

....

Compute the remaining cylinders and add them up to get the approximation.

Good luck!!