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The work-energy theorem states that the work done by non-conservative forces equals the change of the object's kinetic energy:
 
W = ΔKE
 
Now use the definitions of work and KE:
 
W = F Δx ,  ΔKE = KEf - KEi = ½m(vf2-vi2)
 
so that
 
F Δx = ½m(vf2-vi2)
 
F = ½(1300 kg) ((20m/s)²-0)/(80m) = 3,300 N
 
(I'm assuming 2 significant digits, though it could be just 1.)

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