square foot is a unit of area. find the area of the manhole. A = (pi)r^2
9.2 lbs per square foot multiplied by area in units of square feet gives lbs.
diameter is twice radius, so radius is 1.5 ft.
Area of manhole = (pi)(1.5)^2
lbs manhole = (9.2)(pi)(1.5)^2
= 65 lbs
