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

for women
for men,

where a represents the person’s age. if the desirable heart rate for a man is 135 beats per minute, how old is he?

a.
22.5 years old
b.
40 years old
c.
45 years old
d.
42.5 years old

select the best answer from the choices provided