Let f(x) represents the heart beat of the person.
Now, we have been given that person’s theoretical maximum heart rate is given by 220 - x.
Also, we have been given that person strive for a heart rate that is at least 50% of the maximum. At least means greater than equal to.
Thus, we have
Also, we have been given that person strive for a heart rate that is at most 75% of the maximum. At most means less than equal to.
Therefore, the system of inequality is given by