Answer:
Problem 1) frequency: 160 heartbeats per minute, period= 0.00625 minutes (or 0.375 seconds)
Problem 2) Runner B has the smallest period
Problem 3) The sound propagates faster via a solid than via air, then the sound of the train will arrive faster via the rails.
Step-by-step explanation:
The frequency of the football player is 160 heartbeats per minute.
The period is (using the equation you showed above):

second problem:
Runner A does 200 loops in 60 minutes so his frequency is:
loops per minute
then the period is: 0.3 minutes (does one loop in 0.3 minutes)
the other runner does 200 loops in 65 minutes, so his frequency is:
loops per minute
then the period is:

Therefore runner B has the smaller period
Answer:
steps below
Step-by-step explanation:
post here 16 and 17, should be able to do 18 and 19 yourself
16.
y=-8 for x≤-6
y=-1/4 x + 2 for -4≤x≤4
y=4 for x>4
17.
y=-x-4 for x<-3
y=x+1 for -3≤x≤1
y=-6 for x>4
Answer:
a>6
Step-by-step explanation:
add 2 to both sides