F6 problem solving

(1) Water in tank.
Sketch a graph that depicts the amount of water in a 100 gal tank.
The tank is initially empty and then filled at a rate of 5 gal per minute.
Immediately after it is full, a pump is used to empty the tank at 2 gal per minute.


(2) Distance from Home.
Sketch a graph showing the distance a person is from home after x hours,
if he drives on a straight road at 40 mph to a park 20 mi away,
remains at the park for 2 hour,
and then returns home at a speed of 20 mph.


(3) Alternating Electric Current.
The study of alternating electric current requires the solutions of equations
i=I_max sin2(pi)ft,
for time t in seconds,
where i is instantaneous current in amperes,
I_max is maximum current in amperes,
and f is the number of cycles per second.
Find the least positive value of t, given i=I_max, f=60.