Answer:
Estimation
Step-by-step explanation:
You can tell your grandma that she can find her target heart rate by finding the maximum heart rate. Heart rate is the amount of times your heart beats in a minute.
An example is: subtracting 220 from your age can give you your maximum heart rate. Putting your hand on your wrist and counting the amount of beats that happen within a one minute timer will give you your current heart rate.