Do the calculations slowly - find the volume, the mass, 
and the weight of each thin "slice" of water, then compute 
the work needed to lift it to the spout, 
then write the total work for pumping the water 
out of the tank as a limit of Riemann sums, 
and finally represent this limit as a definite integral 
and find the value of the definite integral.  
Introduce notations, say A=3m for the depth, 
B=3m for the width, and H=2m for the height of the spout 
above the top of the tank, and work out your answer 
in terms of these three quantities (and also the density 
"rho" of the water and the gravity acceleration, g).  
Do NOT replace A, B, H, rho, and g by their numerical values 
while you are solving the problem, but only after you 
obtained the answer in terms of these quantities.  
It is a good idea to check the units at each step; 
the units of these quantities are 
   * units for A, B, H: meters,
   * unit for rho : kilogram per cubic meter, 
   * unit for g: meter per (second squared).