Medical researchers have determined that for exercise to be beneficial, a person’s desirable heart rate, r, in beats per minute, can be approximated by the formulas

r=143-0.65a for women
r=165-0.75a for men,

where a represents the person’s age. what would the desirable heart rate be for a 46 year old woman?
a. 113 beats per minute
b. 172.9 beats per minute
c. 143.7 beats per minute
d. 63 beats per minute