Four people are pulling a float to maintain a constant speed of 3.0 km/h for the float. Two people pull with a force of 210 n each and the other two pull with a force of 140n each. Whata is the force of friction between the float and the ground?

Hint - if an object maintains a constant speed that means it is not accelerating. From \Sigma F = ma this means that the sum of forces is zero. So - what do you think the answer is?