Explanation:
I assume it means the task is filled completely.
diameter = 2.1 m
therefore, radius = diameter/2 = 2.1/2 = 1.05 m
height = 4 m
volume of a cylinder is
ground area × height, so
pi×r² × height = pi×1.05²×4 = 13.8544236... m³
1 cm³ is 1g
for 1 kg (remember, "k" stands for "kilo" and means 1000) we need therefore 1000 cm³ (which is a cube of 10 cm side length).
how many cm³ are in 13.8544236... m³ ?
1 m = 100 cm
1 m² = 1 m × 1 m = 100×100 = 10,000 cm²
1 m³ = 1 m × 1 m × 1 m = 100×100×100 = 1,000,000 cm³
that means a factor of 1,000,000 !
so, the volume of the cylinder is
13.8544236... × 1,000,000 = 13,854,423.6... cm³
to get the mass of kg of that much water we need now to divide by 1000 :
13,854,423.6... / 1000 = 13,854.4236... kg
which is, by the way, 13.8544236... tons.
yes, 1 m³ of water is 1 ton ...
I don't know, if you need to round the result.
if you e.g. only need full kg, then the answer would be
13,854 kg.