Please include the equations you use

The independent variable would be the fertilizer as it is what the dependent variable (the growth of grass) depends on.

I'm having some difficulty seeing the diagram clearly.but the question says there's a net inward force on the object.so we know right away,  from newton's 2nd law of motion, thatthat baby is accelerating.  it doesn't even matter which way thenet force is pointing.  if there's any net force, then either theobject's speed or else its direction must be changing.

You need to calculate the string in between two masses

The answer is mean don't know