the difference quotient is just the slope form, in a variation
so that should be (f(x+h)-f(x))/h as x approaches 0
the 2nd option is the differnce quotient, but with the negative distributed
the 3rd option is really f(x)-f(5) because f(5)=61 and that is valid
4th option is wrong because it is (f(x+h)+f(x))/h instead of (f(x+h)-f(x))/h
answer is 4th option
