Need a little help with this one

Which expressions are equivalent to -6 + 3m

For f(x) = 3x+1 and g(x) = x2 - 6, find (g/f)(x)

Afarmer has a large field that is x feet in length. he wants to fence in a rectangular section in the middle of the field , leaving a length of 100 feet of open field behind each end of the fenced rectangle.he also wants the width of the fenced-in space to be 100 feet less than its length. find the expressions to represent the length and width of the fenced section of the field