An aquarium contains water weighing 62.4lb/ft^3. The Aquarium of a cub where the length of each edge is 3ft. What is the force exerted by the water pressure on each vertical side of the tank?

To find pressure, what I did was 62.4x3=187.2 (p=wh)

Then to find force I did 187.2x9=1684.8 N (F=pressure x area)

However my book says the answer is 842.4 lb

What did I do wrong and please explain to me how I get the answer thank you.