A rocket is projected directly upward with an initial velocity of 352 ft/sec from the ground. After t seconds, it's height in feet is given by f(t) = -16t^2 + 352t. After how many seconds will it be 640 feet above the ground?

Two farmers pay a total rent of $140 for a pasture. the first farmer placed $4 oxen in the pasture, and the second farmer placed $30 sheep in the pasture. the farmers split the rent based on the proportion of the pasture eaten by their own animals that month. how much should the first farmer pay, if 1 ox eats as much as 10 sheep in a month?