To determine how much weight the water adds to the tank, we'll follow these steps:
1. Identify the tank's capacity in gallons and the weight per gallon of water:
- Tank capacity: 643.18 gallons
- Weight per gallon of water: 8.34 lbs/gallon
2. Calculate the total weight of the water:
- The total weight can be found by multiplying the tank's capacity by the weight of one gallon of water.
[tex]\[
\text{Total Weight} = \text{Tank Capacity} \times \text{Weight per Gallon}
\][/tex]
Substituting the given values:
[tex]\[
\text{Total Weight} = 643.18 \text{ gallons} \times 8.34 \text{ lbs/gallon}
\][/tex]
3. Perform the multiplication to find the total weight of the water:
[tex]\[
\text{Total Weight} = 5364.1212 \text{ lbs}
\][/tex]
4. Round the result to two decimal places:
[tex]\[
\text{Total Weight Rounded} = 5364.12 \text{ lbs}
\][/tex]
Based on these calculations, the weight added by the water to the tank is:
[tex]\[
\boxed{5364.12 \text{ lbs}}
\][/tex]
So the correct answer is:
b. 5364.12 lbs.