(a)
Because there is 3.5 kg of copper in the original mix, then the maximum amount of copper that can be removed is 3.5 kg, in that case, x would be equal to -3.5 and the percentage of copper would be 0%. Then, (-3.5, infinity) interval is the domain. When 3.5 kg of copper are removed, f(x) = 0%, and in the limit when x tends to infinity, f(x) = 100%. So, the range is 0% to 100%.
(b)
The percentage of copper in the mix, f(x) = 100*(3.5 + x)/(7 + x)
where x is kg of copper that are add (x>0) or removed (x<0)
(c)
In this case, the domain of the function is every real number except -7, i. e., (-infinity, -7) U (-7, infinity) interval.
The range of a rational function where the grade of the polynomial in the numerator is less or equal than the grade of the polynomial in the denominator is all real numbers, i. e., (-infinity, infinity) interval.
