water tank is 10 gallon
it has a leak rate of 0.035 gallon per day
auto-refill kicks in when water drops to 4 gallon
let d be the number of days before auto-refill kicks in
10-0.035d=4
a balloon's volume is 10L and I want it to be 4L.
if I let the air out at 0.035L per minutes, how many minutes I have wait?
d is the minutes then 10 - 0.035*d = 4