I'm having a hard time with understanding this
First of all Please don't put everything in bold. The whole point of putting something in bold is to give it emphasis and make it stand out, but if everything is in bold then what is the point... because now nothing stands out, and it is fairly more difficult on the eyes that way and less pleasant to read. Also just leave the Homework template headers the way they are and fill in your information under them, look at some other posts to see what I mean.
Well the first one is simple, the maximum force is 21750N and the mass is 2100kg, your equation is correct.
Just find "a" the acceleration, if 21750N is the maximum then that is the value you want because if it were greater it would break, and if it were any less then it would not be the maximum would it? So you need exactly the acceleration of the 2100kg mass that will give you 21750N of force.
F = ma, so 21750N = 2100kg * a
Maybe you can solve the others on your own now.
Thanks :) I edited it already. Sorry for that.
Separate names with a comma.