Refers to the number of exercise sessions per week-for example, three to five times per week.

Frequency

Explanation:

Frequency refers to the counts of events per amount of time of a repeated case. The amount of times a data and insights happens is a frequency. A given data value's rate is the amount of times that data value happens.

In this situation number of days count as frequency

sonar - device which is used to find the submit submarines, sankalp ship. sonar waves consists of a transmitter and detector which are installed in the observation centre on board of a ship. the ultrasonic waves are sent into the sea at high frequency about 1000 khz in all direction.

i believe the answer is a