ok so we are at 1 full pool by the end of both right? so we need the rate of both hoses. well, if I do 1/90 I find out how much is flowing into the pool per minute. Same with the other where it is 1/35/minute so together, we set up this equation

1/90+1/35=5/126 So 5/126 of the tank is filled per minute. So now we need how many minutes until we get to 126. SO 126/5 minutes is our answer.