An explosion causes debris to rise vertically with an initial velocity of 160 feet per second. what is the speed of debris when the height is 300 feet? i am using the formula: -16t^2 + vot + h0 because the question is referring to feet.

The question is asking what v_final is, given that v_initial is at 300 feet. and v_initial is at 0 feet.  
We know there will be a constant downward acceleration of 32.15 ft/s^2.
 Use the following equation: 
 v_final^2 = v_initial^2 + 2ah
 v_final^2 = (160 ft/s)^2 + 2(-32.15 ft/s^2)(300 ft) = 6310 ft^2/s^2
 v_final = (6310 ft^2/s^2)^1/2 = 79.4 ft/s.