The landscaper pours 150 gallons of herbicide in a pond. The herbicide degrades 9% each week. Write an equation to find the amount of herbicide in any given week. y = ( _________ ) t , t = number of...

The landscaper pours 150 gallons of herbicide in a pond. The herbicide degrades 9% each week.

Write an equation to find the amount of herbicide in any given week.

y =  ( _________ )^t, t = number of weeks

How much will be in the pond after 2 weeks?

    ___________ (round to the nearest gallon)

The landscaper will put another dose in the pond when the herbicide level drops below 50 gallons. In about how many weeks will he need to add more herbicide?

   ____________weeks