Aclam of mass 0.12 kg dropped by a seagull takes 3.0 s to hit the ground. [neglect friction.]
***what is the force that the clam exerts on the ground upon impact? [show all work, including the equation and substitution with units.***

This is a defective, misleading question, and should never be asked in a Physics class.

There is no such thing as the force due to the impact.

If you know how long it takes the clam to stop once it begins to hit the dirt,
then you can calculate the impulse transferred to it, and tease a force out
of that.  But the question doesn't give us the time. 

It depends on the material of the surface.  Was the clam dropped onto dirt ? 
Into a dumpster ?  Onto grass ?  Concrete ?  Styrofoam ?  Mud ?  The answer
is different in each case, and we still need to know the short length of time
AFTER it first encountered whatever surface brought it to rest.

I would kick this question back to the Physics teacher.  It's meaningless,
and the longer you try to work on it, the more nonsense you'll plant into
your head that'll need to be dug out later.

The answer is a 0.64 volts